阅读下面的短文，从每题所给的四个选项(A、B、C、D)中，选出最佳选项。
E
What makes a person a scientist? Does he have ways or tools of learning that are different from those of others? The answer is“No”. It is not a tool a scientist uses but how he uses these tools that makes him a scientist. You will probably agree that knowing how to use a power is important to a carpenter. You will probably agree, too, that knowing how to investigate, how to discover information, is important to everyone. The scientist, however, goes one step further：he must be sure that he has a reasonable answer to his question into a large set of ideas about how the world works.
The scientist's knowledge must be exact. There is no room for half right or right just half the time. He must be as nearly right as the conditions permit. What works under one set of conditions at one time must work under the same conditions at other times. If the conditions are different, any change file scientist observes in a demonstration must be explained by the change in the conditions.
This is one reason that investigations are important in science. Albert Einstein, who developed the theory of relativity, arrived at this theory through mathematics. The accuracy of his mathematics was later tested through investigation. Einstein's ideas are shown to be correct. A scientist uses many tools for measurements. Then the measurements are used to make mathematical calculations that may test his investigations.
“...knowing how to investigate, how to discover information, is important to everyone.”The author says this to show________.

A．the importance of information

B．the difference between carpenters and ordinary people

C．the difference between scientists and ordinary people

D．the importance of thinking

A sound scientific theory should be one that________.

A．works under one set of conditions at one time and also works under the same conditions at other times

B．leaves no room for improvement

C．does not allow any change even under different conditions

D．can be used for many purposes

What is the main idea of the passage?

A．Scientists are different from the ordinary people.

B．The theory of relativity.

C．Exactness is the secret of science.

D．Exactness and way of using tools is the key to the making of a scientist.