During the 19th century, scientists found that when certain parts of the brain of a person were hurt, he would lose the power of doing certain things. And so people thought that each part of the brain does a different job. But modern research has discovered that this is not so, for it is not easy to show exactly what each part of the brain does.
In the past fifty years there has been a great increase in the amount or research done on the brain. Scientists have found out that the way the brain works is not so simple as people in general may think. Chemists tell us that about 100,000 chemical changes take place in the brain every second. Some recent researches also suggest that we can remember everything that happened to us. We may not be able to think of the things we have heard and seen but it is kept there in the store-house of the human mind. Earlier scientists thought that the power of one’s brain got weaker and weaker as one grows older. But it is plenty of exercise, it keeps its power. It is now thought that is not true. As long as the brain is given plenty of exercise, it keeps its power. It has proved that an old person who has always been active in the mind has a quicker mind than a young person who has done physical work without using much of his brain.
In the last century, scientists found that a person would lose the power to do certain things _____.

A．when he got weaker in health

B．if certain parts of his brain were hurt

C．after he did a quite different job

D．when he grew older

Scientists today are still unable to show exactly ______.

A．what each part of the brain is doing

B．how many chemical changes take place in the brain each second

C．whether each part of the brain does the same job

D．which part of the brain is the most important

It has been found that one’s brain usually works ______.

A．faster when he is old

B．a little now and a little then

C．in a very simple way

D．without any rest all day long

Which of the following is NOT true according to the text?

A．Scientists are working hard at the researches on the brain.

B．As many as six million chemical changes take place in the brain every minute.

C．A young man doing physical labor is sure to have a much slower mind.

D．Even an old man has a quick mind only if his brain is given much exercise.

The more work we give our brains,___________.

A．the less result we will gain

B．the more work they are able to do

C．the weaker their power will get

D．the more tired they will feel