2. How was the first permanent picture made?

　 A. By making use of special paper.　　　　　　　 B. By adding common salt to silver salt.

　 C. By giving a slight colour to the silver salt.　　　 D. By using a special piece of metal.

1. What discovery was the basis of photography?

　 A. Light darkens silver salt.　　　　　　　　　　 B. Light darkens natural salt.

　 C. Light darkens silver.　　　　　　　　　　　　 D. Light darkens self--developing film

49、(1分)

　　 Today I’ll be talking about the invention of the camera and photography. The camera is often thought to be a modern invention, but as early as 1727, a German physicist discovered that light darkens silver salt. Used as a camera, a big box was set up, and a small hole was cut in one side to let the light in; he made temporary pictures on the salt. Silver salt is still the base of the photographic film today. Then a French scientist made the first permanent (永久的) picture by using a special piece of metal which was covered with silver salt. A photograph he made in 1826 still exists.

　　 The painter De Gear improved the process (制作法) by covering the metal also with placing the common salt which we can eat. This was in 1839, the official date of beginning of photographs. But the problem was the printing of the photographs. And it wasn’t until other scientists developed the kind of photographic paper we now use that good prints were possible and photography became truly modern. In the 1870’s, Matthew Bradey was able to take his famous pictures in American Civil War. In the 20’s of this century, Georges Mann of the United States simplified film developing (冲洗), and Dr Edward Lane invented the so-called ‘Instant Camera’ which uses self-developing film. If we say photography came into existence in 1839, it follows that it took more than 100 years for the camera to reach its present condition of technical refinement(密度).

5. The best title (题目) for the passage is

　 A. A Strange Continent　　　　　　　　　 B. An Ice Continent

　 C. Snowfall at the South Pole　　　　　　　 D. The World’s Desert

4. The snow turns to ice when

　 A. it gets wet.　　　　　　　　　　　　 B. the next snowfall comes.

　 C. the temperature gets colder.　　　　　　 D. the snow above it is heavy enough.

3. The snow in Antarctica is very deep because it

　 A. never stops falling.　　　　　　　　　 B. piles up year after year.

　 C. never melts.　　　　　　　　　　　　 D. both B and C.

2. Antarctica has

　 A. ten times as much moisture as the Sahara.

　 B. the same amount of moisture as the Sahara.

　 C. about one-tenth of the moisture of the Sahara.

　 D. none of the above.

1. Antarctica is called a desert because it

　 A. is sandy.　　　　　　　　　　　　　　　 B. has the same temperature as a desert.

　 C. has little moisture and no lakes or rivers.　　 D. there are no people there.

48、(1分)

　　 The Antarctica is a actually a desert. It is the only continent on the earth without a river or a lake.

　　 The Antarctica is all ice all year round. The warmest temperature ever recorded (所记录的) there is zero, at the South Pole. Explorers (探险家) used to think that a place so cold would have a heavy snowfall. But less than ten inches of snow falls each year. That is less than half an inch of water. Ten times that much moisture (水份) falls in parts of the Sahara.

　　 The little snow that falls in Antarctica never melts (融化). It continues to pile up deeper and deeper year after year and century after century. When the snow gets to be about eighty feet deep it is turned to ice by the weight of snow above it .

5. We can guess from the passage that

　 　A. Jack was as poor at history as Paul.　　 B. Jack was as good at history as Paul.

　 C. Jack was better at history than Paul.　　 D. Jack was poorer at history than Paul.