Question

【题目】 If the salinity of ocean waters is analyzed, it is found to vary only slightly from place to place. Nevertheless, some of these small changes are important. There are three basic processes that cause a change in oceanic salinity. One of these is the subtraction of water from the ocean by means of evaporation--conversion of liquid water to water vapor. In this manner, the salinity is increased, since the salts stay behind. If this is carried to the extreme, of course, white crystals of salt would be left behind.

The opposite of evaporation is precipitation(降水), such as rain, by which water is added to the ocean. Here the ocean is being diluted(稀释) so that the salinity is decreased. This may occur in areas of high rainfall or in coastal regions where rivers flow into the ocean. Thus salinity may be increased by the subtraction of water by evaporation, or decreased by the addition of fresh water by precipitation or runoff.

Normally, in tropical regions where the sun is very strong, the ocean salinity is somewhat higher than it is in other parts of the world where there is not as much evaporation. Similarly, in coastal regions where rivers dilute the sea, salinity is somewhat lower than in other oceanic areas.

A third process by which salinity may be altered is associated with the formation and melting of sea ice. When seawater is frozen, the dissolved materials are left behind. In this manner, seawater directly beneath freshly formed sea ice has a higher salinity than it did before the ice appeared. Of course, when this ice melts, it will tend to decrease the salinity of the surrounding water.

In the Weddell Sea, off Antarctica, the densest water in the oceans is formed as a result of this freezing process, which increases the salinity of cold water. This heavy water sinks and is found in the deeper portions of the oceans of the world.

【1】What is the best title for the passage?

A.Typical Oceans and Their Respective Features

B.The Causes of the Changes in Salinity of Ocean Water

C.Different Oceans Have Different Salinity

D.The Precipitation and Evaporation of Oceans

【2】Which of the following processes will increase salinity of ocean waters?

A.EvaporationB.Precipitation

C.MeltingD.Dilution

【3】According to this passage, the sea ________ is likely to have the lowest salinity.

A.in tropical areasB.off Antarctica

C.of high rainfallD.with abundant

【4】The Weddell Sea _______.

A.is an example of increased salinity in freezing sea water

B.is much larger in area than the Arctic oceans

C.has a much lower salinity now than ever

D.has the denser water in its upper parts

Answer 1

【答案】

【1】B

【2】A

【3】C

【4】A

【解析】

本文是一篇说明文，介绍了造成海水盐度变化的原因。

【1】主旨大意题。通读全文，特别是根据第一段中的“There are three basic processes that cause a change in oceanic salinity.”可知，造成海洋盐度变化的基本过程有三个。所以本文主要介绍了造成海水盐度变化的原因，故短文的最佳标题为“海水盐度变化的原因”。故B项正确。

【2】细节理解题。根据第二段中的“Thus salinity may be increased by the subtraction of water by evaporation”可知，因此，盐度可以通过蒸发减少水分来增加。所以蒸发会使海水盐度增加，故A项正确。

【3】推理判断题。根据第二段中的“The opposite of evaporation is precipitation(降水), such as rain, by which water is added to the ocean. Here the ocean is being diluted(稀释) so that the salinity is decreased.”可知，降水会使海水的盐度降低，因此，降雨量大的海水的盐度可能最低，故C项正确。

【4】细节理解题。根据最后一段中的“In the Weddell Sea, off Antarctica, the densest water in the oceans is formed as a result of this freezing process, which increases the salinity of cold water.”可知，在南极洲边缘的威德尔海中，结冰过程增加低温海水的盐度，从而形成了浓度最大的海水，由此可知，威德尔海是海水结冰时盐度增加的一个例子，故A项正确。

主旨大意题的难度较大，对文章主题句的把握是关键，科普类说明文一般第一段就会点明主题，例如本篇第1题，通读全文，特别是根据第一段中的“There are three basic processes that cause a change in oceanic salinity.”可知，造成海洋盐度变化的基本过程有三个，由此可知，本文主要介绍的是造成海水盐度变化的原因，故短文的最佳标题为“海水盐度变化的原因”。故B项正确。