3. When the fiddler crabs were kept in the dark , they ______.

　 A. did not change colour　　　　　　 B. changed colour more quickly

　 C. changed colour more slowly　　　　 D. changed colour on the same timetable

2. The crab’s changing colour ______.

　 A. tells the crab what time it is　　　　 B. protects the crab from the sunlight and enemies

　 C. keeps the crab warm　　　　　　　 D. is of no real use

1. The fiddler crab is like a clock because it changes colour ______.

　 A in a regular 24-hour rhythm　　　　　　 B. in answer to the sun’s rays

　 C. at low tide　　　　　　　　　　　　　　 D. every fifty minutes

50、(1分)

　　 The fiddler crab (蟹) is a living clock. It indicates(=shows) the time of day by the colour of its skin, which is dark by day and pale by night. The crab’s changing colour follows a regular twenty-four hour plan that exactly matches the daily rhythm (节奏) of the sun.

　　 Does the crab actually keep time, or does its skin simply answer to the sun’s rays, changing colour according to the amount of light strikes it? To find out, biologists kept crabs in a dark room for two months. Even without daylight, the crab’s skin colour continued to change exactly on time.

　　 This characteristic (特性) probably developed gradually in answer to the daily rising and setting of the sun, to help protect the crab from sunlight and enemies. After millions of years it has become completely regulated (受控制) inside the living body of the crab.

　　 The biologists noticed that once each day the colour of the fiddler crab is especially dark, and that each day this happens fifty minutes later than on the day before. From this they discovered that each crab follows not only the rhythm of the sun but also that of the tides (潮水). The crab’s period of greatest darkening is exactly the time of low tide on the beach where it was cought!

5. What did Doctor Edward Lane invent?

　 A. A cheap process of developing film at home.

　 B. A new kind of film.

　 C. An automatic printer.

　 D. An ‘instant camera’ that develops its own film.

4. According to the speaker why is Matthew Bradey remembered today?

　 A. He was a soldier.　　　　　　　　　 B. He took war photographs.

　 C. He painted portraits.　　　　　　　　 D. He designed a portable camera.

3. What does the speaker regard as the official date of beginning of photography?

　 A. 1727　　　　　 B. 1826　　　　　　 C. 1839　　　　　　 D. 1870

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).