Have you ever noticed the colour of the water in a river or stream after a heavy rainfall? What do you think caused this change in colour? It is soil that has been washed into the river from the riverbank or from t}le nearby fields．

Components of Soft

Soil is made up of a number of layers（层），each having its own distinctive colour and texture．The upper layer is known as the litter．It acts like a blanket．limiting temperature changes and reducing water loss．The topsoil layer is made up of small particles of rock mixed with rotten plant and animal matter called humus（腐殖质），which is black and gives the topsoil its dark colour．This layer is usually rich in nutrients，oxygen，and water．Below the topsoil is the subsoil，a layer that contains more stones mixed with only small amounts of organic matter．This layer is lighter in colour because of the lack of humus．Beneath the soil lies a layer of bedrock．

Soil forms from the bottom up．Over time bedrock is attacked by rain, wind，frost, and snow．It is gradually broken down into smaller particles in a process called weathering．Plants begin to grow，and rotten materials enrich the topsoil．Most of the soil in Eastern Canada．for example．Was formed from weathered rock that was exposed when the ice disappeared l2．000 years ag0．

Water Beneath the Soil

Surface water collects and flows above the ground in lakes．ponds．and rivers．Once in the soil or rock，it is called groundwater．Gravity pulls groundwater through the soil in a process called percolation（渗透）．Eventually the water reaches a layer called the water table．Under this is bedrock through which water cannot percolate．

As water percolates downward，it dissolves organic matter and minerals from the soil and carries them to deeper layers．This causes a serious problem because plants require these nutrients for growth.

Soil pH

Soil can be acidic．neutral．or basic．The pH of the soil is determined by the nature of the rock

from which it was formed．and by the nature of t}le plants that grow and rot in it．

The acidity of rain and snow can lower the pH of the groundwater that enters the soil．By burning fossil fuels such as coal，oil and gasoline，humans have been contributing to higher levels of acidity in many soils．When fossil fuels are burned．gases are released into the air and then fall back to earth as acid rain．Acid soil increases出e problem of carrying nutrients to lower soil levels．As nutrients are removed，soil is less fertile．Plants grow more slowly in acidic soil，and also become easily attacked by diseases．

1.The layer of soil that provides necessary nutrients for plant growth is called．

A．1itter    B．topsoil    C．humus D．subsoil

2.According to the text．which of the following is NOT true?

A．Soil forms from weathered rock on the earth surface．

B．The deeper layer of soil is darker in colour than t}le surface soil．

C．Air pollution is partially responsible for acid soil．

D．Groundwater tends to carry away nutrients for plant growth．

3.We can infer from the passage that the water table lies       ．

A．between the topsoil layer and the subsoil layer

B．in the subsoil layer above bedrock

C．between the subsoil layer and bedrock

D．in the bedrock layer beneath the subsoil

4.The underlined word “dissolve” is used to express the idea that organic matter and minerals from soil are          ．

A．rushed away into the river

B．cleaned and purified by water

C．destroyed and carried away by water

D．mixed with water and become part of it

Have you ever noticed the colour of the water in a river or stream after a heavy rainfall? What do you think caused this change in colour? It is soil that has been washed into the river from the riverbank or from t}le nearby fields．
Components of Soft
Soil is made up of a number of layers（层），each having its own distinctive colour and texture．The upper layer is known as the litter．It acts like a blanket．limiting temperature changes and reducing water loss．The topsoil layer is made up of small particles of rock mixed with rotten plant and animal matter called humus（腐殖质），which is black and gives the topsoil its dark colour．This layer is usually rich in nutrients，oxygen，and water．Below the topsoil is the subsoil，a layer that contains more stones mixed with only small amounts of organic matter．This layer is lighter in colour because of the lack of humus．Beneath the soil lies a layer of bedrock．
Soil forms from the bottom up．Over time bedrock is attacked by rain, wind，frost, and snow．It is gradually broken down into smaller particles in a process called weathering．Plants begin to grow，and rotten materials enrich the topsoil．Most of the soil in Eastern Canada．for example．Was formed from weathered rock that was exposed when the ice disappeared l2．000 years ag0．
Water Beneath the Soil
Surface water collects and flows above the ground in lakes．ponds．and rivers．Once in the soil or rock，it is called groundwater．Gravity pulls groundwater through the soil in a process called percolation（渗透）．Eventually the water reaches a layer called the water table．Under this is bedrock through which water cannot percolate．
As water percolates downward，it dissolves organic matter and minerals from the soil and carries them to deeper layers．This causes a serious problem because plants require these nutrients for growth.
Soil pH
Soil can be acidic．neutral．or basic．The pH of the soil is determined by the nature of the rock
from which it was formed．and by the nature of t}le plants that grow and rot in it．
The acidity of rain and snow can lower the pH of the groundwater that enters the soil．By burning fossil fuels such as coal，oil and gasoline，humans have been contributing to higher levels of acidity in many soils．When fossil fuels are burned．gases are released into the air and then fall back to earth as acid rain．Acid soil increases出e problem of carrying nutrients to lower soil levels．As nutrients are removed，soil is less fertile．Plants grow more slowly in acidic soil，and also become easily attacked by diseases．
【小题1】The layer of soil that provides necessary nutrients for plant growth is called．

Have you ever noticed the colour of the water in a river or stream after a heavy rainfall? What do you think caused this change in colour? It is soil that has been washed into the river from the riverbank or from t}le nearby fields．

Components of Soft

Soil is made up of a number of layers（层），each having its own distinctive colour and texture．The upper layer is known as the litter．It acts like a blanket．limiting temperature changes and reducing water loss．The topsoil layer is made up of small particles of rock mixed with rotten plant and animal matter called humus（腐殖质），which is black and gives the topsoil its dark colour．This layer is usually rich in nutrients，oxygen，and water．Below the topsoil is the subsoil，a layer that contains more stones mixed with only small amounts of organic matter．This layer is lighter in colour because of the lack of humus．Beneath the soil lies a layer of bedrock．

Soil forms from the bottom up．Over time bedrock is attacked by rain, wind，frost, and snow．It is gradually broken down into smaller particles in a process called weathering．Plants begin to grow，and rotten materials enrich the topsoil．Most of the soil in Eastern Canada．for example．Was formed from weathered rock that was exposed when the ice disappeared l2．000 years ag0．

Water Beneath the Soil

Surface water collects and flows above the ground in lakes．ponds．and rivers．Once in the soil or rock，it is called groundwater．Gravity pulls groundwater through the soil in a process called percolation（渗透）．Eventually the water reaches a layer called the water table．Under this is bedrock through which water cannot percolate．

As water percolates downward，it dissolves organic matter and minerals from the soil and carries them to deeper layers．This causes a serious problem because plants require these nutrients for growth.

Soil pH

Soil can be acidic．neutral．or basic．The pH of the soil is determined by the nature of the rock

from which it was formed．and by the nature of t}le plants that grow and rot in it．

The acidity of rain and snow can lower the pH of the groundwater that enters the soil．By burning fossil fuels such as coal，oil and gasoline，humans have been contributing to higher levels of acidity in many soils．When fossil fuels are burned．gases are released into the air and then fall back to earth as acid rain．Acid soil increases出e problem of carrying nutrients to lower soil levels．As nutrients are removed，soil is less fertile．Plants grow more slowly in acidic soil，and also become easily attacked by diseases．

67．The layer of soil that provides necessary nutrients for plant growth is called．

A．1itter    B．topsoil    C．humus D．subsoil

68．According to the text．which of the following is NOT true?

A．Soil forms from weathered rock on the earth surface．

B．The deeper layer of soil is darker in colour than t}le surface soil．

C．Air pollution is partially responsible for acid soil．

D．Groundwater tends to carry away nutrients for plant growth．

69．We can infer from the passage that the water table lies       ．

A．between the topsoil layer and the subsoil layer

B．in the subsoil layer above bedrock

C．between the subsoil layer and bedrock

D．in the bedrock layer beneath the subsoil

70．The underlined word “dissolve” is used to express the idea that organic matter and minerals from soil are          ．

A．rushed away into the river

B．cleaned and purified by water

C．destroyed and carried away by water

D．mixed with water and become part of it

Have you ever noticed the colour of the water in a river or stream after a heavy rainfall? What do you think caused this change in colour? It is soil that has been washed into the river from the riverbank or from t}le nearby fields．

Components of Soft

    Soil is made up of a number of layers(层)，each having its own distinctive colour and texture．The upper layer is known as the litter．It acts like a blanket．limiting temperature changes and reducing water loss．The topsoil layer is made up of small particles of rock mixed with rotten plant and animal matter called humus(腐殖质)，which is black and gives the topsoil its dark colour．This layer is usually rich in nutrients，oxygen，and water．Below the topsoil is the subsoil，a layer that contains more stones mixed with only small amounts of organic matter．This layer is lighter in colour because of the lack of humus．Beneath the soil lies a layer of bedrock．

    Soil forms from the bottom up．Over time bedrock is attacked by rain, wind，frost, and snow．It is gradually broken down into smaller particles in a process called weathering．Plants begin to grow，and rotten materials enrich the topsoil．Most of the soil in Eastern Canada．for example．Was formed from weathered rock that was exposed when the ice disappeared l2．000 years ag0．

Water Beneath the Soil

    Surface water collects and flows above the ground in lakes．ponds．and rivers．Once in the soil or rock，it is called groundwater．Gravity pulls groundwater through the soil in a process called percolation(渗透)．Eventually the water reaches a layer called the water table．Under this is bedrock through which water cannot percolate．

    As water percolates downward，it dissolves organic matter and minerals from the soil and carries them to deeper layers．This causes a serious problem because plants require these nutrients for growth.

Soil pH

    Soil can be acidic．neutral．or basic．The pH of the soil is determined by the nature of the rock

from which it was formed．and by the nature of t}le plants that grow and rot in it．

    The acidity of rain and snow can lower the pH of the groundwater that enters the soil．By burning fossil fuels such as coal，oil and gasoline，humans have been contributing to higher levels of acidity in many soils．When fossil fuels are burned．gases are released into the air and then fall back to earth as acid rain．Acid soil increases出e problem of carrying nutrients to lower soil levels．As nutrients are removed，soil is less fertile．Plants grow more slowly in acidic soil，and also become easily attacked by diseases．

67．The layer of soil that provides necessary nutrients for plant growth is called．

    A．1itter    B．topsoil    C．humus D．subsoil

68．According to the text．which of the following is NOT true?

    A．Soil forms from weathered rock on the earth surface．

  B．The deeper layer of soil is darker in colour than t}le surface soil．

  C．Air pollution is partially responsible for acid soil．

    D．Groundwater tends to carry away nutrients for plant growth．

69．We can infer from the passage that the water table lies       ．

A．between the topsoil layer and the subsoil layer

B．in the subsoil layer above bedrock

       C．between the subsoil layer and bedrock

       D．in the bedrock layer beneath the subsoil

70．The underlined word “dissolve” is used to express the idea that organic matter and minerals from soil are          ． 

    A．rushed away into the river

    B．cleaned and purified by water

    C．destroyed and carried away by water

    D．mixed with water and become part of it

                     Dropouts for Ph. D. s

  Educators are seriously concerned about the high rate of dropouts among the doctor of philosophy candidates and the consequent loss of talent to a nation in need of Ph. D. s. Some have placed the dropouts loss as high as 50 percent. The extent of the loss was, however, largely a matter of expert guessing. Last week a well-rounded study was published. It was published. It was based on 22,000 questionnaires sent to former graduate students who were enrolled in 24 universities and it seemed to show many past fears to be groundless.

  The dropouts rate was found to be 31 per cent, and in most cases the dropouts, while not completing the Ph. D. requirement, went on to productive work. They are not only doing well financially, but, according to the report, are not far below the income levels of those who went on to complete their doctorates.

  Discussing the study last week, Dr. Tucker said the project was initiated ‘because of the concern frequently expressed by graduate faculties and administrators that some of the individuals who dropped out of Ph. D. programs were capable of competing the requirement for the degree. Attrition at the Ph. D. level is also thought to be a waste of precious faculty time and a drain on university resources already being used to capacity. Some people expressed the opinion that the shortage of highly trained specialists and college teachers could be reduced by persuading the dropouts to return to graduate schools to complete the Ph. D.’

  “The results of our research” Dr. Tucker concluded, “did not support these opinions.”

1).   Lack of motivation was the principal reason for dropping out.

2).   Most dropouts went as far in their doctoral program as was consistent with their levels of ability or their specialities（特性）

3).   Most dropouts are now engaged in work consistent with their education and motivation.

  Nearly 75 per cent of the dropouts said there was no academic reason for their decision, but those who mentioned academic reason cited failure to pass the qualifying examination, uncompleted research and failure to pass language exams. Among the single most important personal reasons identified by dropouts for non-completion of their Ph. D. program, lack of finances was marked by 19 per cent.

  As an indication of how well the dropouts were doing, a chart showed 2% in humanities were receiving $ 20,000 and more annually while none of the Ph. D. ‘s with that background reached this figure. The Ph. D. ‘s shone in the $ 7,500 to $ 15,000 bracket with 78% at that level against 50% for the dropouts. This may also be an indication of the fact that top salaries in the academic fields, where Ph. D. ‘s tend to rise to the highest salaries, are still lagging behind other fields.

  As to the possibility of getting dropouts back on campus, the outlook was glum. The main condition which would have to prevail for at least 25 % of the dropouts who might consider returning to graduate school would be to guarantee that they would retain their present level of income and in some cases their present job.

The author states that many educators feel that

A steps should be taken to get the dropouts back to campus.

B the dropouts should return to a lower quality school to continue their study.

C the Ph. D. holder is generally a better adjusted person than the dropout.

D The high dropouts rate is largely attributable to the lack of stimulation on the part of faculty members.

Research has shown that

A Dropouts are substantially below Ph. D. ‘s in financial attainment.

B the incentive factor is a minor one in regard to pursuing Ph. D. studies.

C The Ph. D. candidate is likely to change his field of specialization if he drops out.

D about one-third of those who start Ph. D. work do not complete the work to earn the degree.

Meeting foreign language requirements for the Ph. D.

A is the most frequent reason for dropping out.

B is more difficult for the science candidate than for the humanities candidate.

C is an essential part of many Ph. D. programs.

D does not vary in difficulty among universities.

After reading the article, one would refrain from concluding that

A optimism reigns in regard to getting Ph. D. dropouts to return to their pursuit of the degree.

B a Ph. D. dropout, by and large, does not have what it takes to learn the degree.

C colleges and universities employ a substantial number of Ph. D. dropouts.

D Ph. D. ‘s are not earning what they deserve in nonacademic positions.

It can be inferred that the high rate of dropouts lies in

A salary for Ph. D. too low.      B academic requirement too high.

C salary for dropouts too high.   D 1,000 positions.