多层螺旋CT多平面重建（MPR）的图像质量高，主要是因为（） A.多层螺旋CT扫描速

甲、乙两企业签订购销合同，甲按约给付对方4万元定金后，乙企业违约。甲企业依法有权要求乙企业给付（）。

A．2万元 

B．4万元 

C．8万元 

D．6万元

以下关于我国领海无害通过制度的表述中错误的是：( )。

A．外国非军用船舶和航空器，享有依法无害通过我国领海的权利

B．外国军用船舶进入我国领海，必须经我国政府批准

C．外国潜水艇和其他潜水器通过我国领海，必须在海面航行，并展示其旗帜

D．外国核动力船舶和载运核物质、有毒物质或者其他危险物质的船舶通过我国领海，必须持有有关证书，并采取特别预防措施

阅读理解

     It is difficult for doctors to help a person with a damaged brain. Without enough blood, the brain

lives for only three to five minutes. More often the doctors can't fix the damage. Sometimes they are

afraid to try something to help because it is dangerous to work on the brain. The doctors might make

the person worse if he operates on the brain.

     Dr. Robert White, a famous professor and doctor, thinks he knows a way to help. He thinks doctors

should make the brain very cold. If it is very cold, the brain can live without blood for 30 minutes. This

gives the doctor a longer time to do something for the brain.

     Dr. White tried his idea on 13 monkeys. First he taught them to do different jobs, and then he

operated on them. He made the monkeys' blood go through a machine. The machine cooled the blood.

Then the machine sent the blood back to the monkeys' brains. When the brain's temperature was 10°

C, Dr. White stopped the blood to the brain. After 30 minutes he turned the blood back on. He warmed

the blood again. After their operations the monkeys were like they had been before. They were healthy

and busy. Each one could still do the jobs the doctor had taught them.

1. The biggest difficulty in operating on the damaged brain is that           .

A. the time is too short for doctors

B. the patients are often too nervous

C. the damage is extremely hard to fix

D. the blood-cooling machine might break down

2. The brain operation was made possible mainly by           .

A. taking the blood out of the brain

B. trying the operation on monkeys first

C. having the blood go through a machine

D. lowering the brain's temperature

3. What is the right order of the steps in the operation?

a. send the cooled blood back to the brain

b. stop the blood to the brain

c. have the blood cooled down

d. operate on the brain

A. a, b, c, d

B. c, a, b, d

C. c, b, d, a

D. b, c, d, a

用手工研磨两块时，（）将量块进行研磨。

A.直接用手捏住

B.装夹在滑板上

C.放入胶木夹具内

简述什么是“索引”。