The plants can ___ carbon dioxide into oxygen.

A．They can buzz in to kill.

B．They can hear the dry plants' cries.

C．They can imitate the plants' crying.

D．They can attack healthy plants in dry, hot weather.

A．She can help the man take care of the plants.

B．Most plants grow better in direct sunlight.

C．The plants need to be watered frequently.

D．The plants should be placed in a shady spot.

A．You can grow vegetables vertically.

B．You can raise plants in a confined area.

C．You can plant a wide variety of plains together.

D．You can enjoy the beautiful scenery.

_______

A．To see what happened to the survivors of the disease.

B．To study animals that can also get infected with the disease.

C．To look for the plants that could cure the disease.

D．To look for the plants that could cure the disease.

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

A．To see what happened to the survivors of the outbreak.

B．To study animals that can also get infected with the disease.

C．To find out where the virus originates.

D．To look for the plants that could cure the disease.

A．The animals over-fertilize the soil.

B．Dead plant roots can't hold the soil together.

C．The wrong types of plants are left standing.

D．There is a buildup of plant and animal matter.

It can be inferred from Paragraph 2 that ________.

A) it is not technical difficulties that prevent the building of nuclear power plants in the U.S.

B) there are not enough safety measures in the U.S. for running new nuclear power plants

C) there are already more nuclear power plants than necessary in the U.S.

D) the American government will not allow Japanese nuclear reactors to be installed in the U.S.