问题 单项选择题

在车床上用两顶尖装夹车削光轴,加工后检验发现中间小、两头大误差,其最可能的原因是()。

A.车床导轨磨损

B.前后两顶尖刚度不足

C.刀架刚度不足

D.工件刚度不足

答案

参考答案:B

阅读理解

阅读理解。

     Sorry to say, our brains naturally start slowing down at the young age of 30. It used to be thought that

this couldn't be helped, but new studies show that people of any age can train their brains to work faster.

"Your brain is a learning machine," says University of California scientist Dr. Michael Merzenich. Given the

right tools, we can train our brains to act like they did when we were younger. All that's required is the

practice designed just for the purpose: a few exercises for the mind.

     Merzenich has developed a computer-based training method to speed up the process (过程) in which the

brain deals with information (positscience.com). Since much of the data we receive comes through speech,

the Brain Fitness Program works with language and hearing to better speed and accuracy (准确性). Over the

course of training, the program starts asking you to distinguish (tell) sounds (between "dog" and "bog", for

example) at an increasingly faster speed. It's a bit like tennis instructor, says Merzenich, hitting balls at you

faster and faster to keep you challenged. You may start out slow, but before long you're pretty quick.

     The biggest finding in brain research in the last ten years is that the brain at any age is highly plastic. If

you ask your brain to learn, it will learn. And it may even speed up while in the process. To keep your brain

young and plastic you can do one of a million new activities that challenge and excite you:playing table tennis

or bridge, doing crossword puzzles, learning a language...."When it comes to preventing ageing, you really do

'use it or lose it'," says Barbara Sahakian, professor at Cambridge University.

1. People's brains _______ according to the new studies.

A. will not start slowing down until the age of 30

B. will start working slowly after the age of 30

C. can work as well as at a young age through certain exercises

D. can not be improved once they start to slow down

2.What can we learn from the text?

A. Using right tools is important for brains' work.

B. Brain research deals with information from the Internet.

C. Dr. Merzenich is a scientist in computer.

D. Many activities can keep our brains young.

3. Which of the following agrees with the writer's idea?

A. The train methods work better for the old.

B. People should use the brain to stop it from ageing.

C. The training of the brain should start at an early age.

D. It is necessary to take part in as many activities as possible.

选择题