It is the business of the scientist to accumulate knowledge about the universe and all

that is in it, and to find, if he is able, common factors which explain the facts that he knows. He chooses, when he can, the method of the "controlled experiment". If he wants to find out the effect of light on growing plants, he takes many plants, as alike as possible. Some he stands in the sun, some in the shade, some in the dark; all the time keeping all other conditions (temperature, moisture, nourishment) the same. In this way, by keeping other conditions constant, and by varying the light only, the effect of light on the plants can be clearly seen. This method can be applied to a variety of situations.In the course of his inquiries the scientist may find what he thinks is one common explanation for an increasing number of facts. The explanation, if it seems consistently to fit various facts, is called a hypothesis. If a hypothesis continues to stand the test of numerous experiments and remains unshaken, it becomes a law.

1.In order to investigate the effect of light on growing plants the scientist____.

A、has to stand in the sun

B、can keep the same plants under different conditions of light

C、takes as many plants as possible

D、both b and c

2.The word "constant" in the first paragraph means____.

A、continual

B、faithful

C、various

D、unchanging

3.What should be kept the same in a "controlled experiment"？ ____

A、All the factors.

B、The common factors.

C、The factor under investigation.

D、All factors except the one being investigated.

4.According to the passage, a hypothesis is____.

A、an explanation for a large number of facts likely to be accepted as a truth

B、a factor which explains the facts already known to the scientist

C、an explanation that stands the test of numerous experiments

D、a common explanation that will definitely become a law