限制直升机最大速度的主要因素是（）.A.颠簸和高度 B.桨尖速度 C.如升力不对称，

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Mr.Coates works in an office in Brighton, England. One Saturday, he went to the office to do some work. When he got on the lift, it stopped between floors. Mr. Coates could not get out of the lift. He started to shout, but no one heard him. Then Mr. Coates remembered that it was a holiday in England. No one was going to come to work until Tuesday!       There was nothing for Mr. Coates to do. He had to wait. With nothing to eat or drink, Mr. Coates slept for most of the time. Early on Tuesday morning, his workmates came into work and found the lift was not working. When the lift was opened, Mr. Coates came out. He was cold, weak, and tired. He had been in the lift for 62 hours!       Now Mr.Coates says, "I only use lifts if they have telephones in them."

1. Why couldn't Mr.Coates get out of the lift? Because              .

[ ]

A. something was wrong with the lift B. it was the weekend C. it was in an office D. it was a holiday

2. In the lift, there was              .

[ ]

A. food B. water C. a telephone D. nothing

3. What did Mr.Coates do in the lift?

[ ]

A. He shouted. B. He slept. C. He waited. D. All of the above.

4. How long was he in the lift?

[ ]

A. For more than two days. B. For the whole Saturday. C. For the weekend. B. Since last Tuesday.

5. According to the story, which of the following is true?

[ ]

A. Now Mr.Coates is a little afraid of taking a lift. B. Now Mr.Coates likes taking a lift. C. Now Mr.Coates never uses lifts. D. Now Mr.Coates only uses lifts if they have no telephones in them.

控制系统的输出拉氏变换与输入拉氏变换在零初始条件下的比值称为（）

甲、乙两块体积相同的物体，它们质量之比是3：2，那么它们的密度之比是______；若把甲截去

2

3

，把乙截去

1

3

后，剩下部分的两物体密度之比是______．

从原料、外购件投入生产起，到经检验合格办完入库手续之前，存在各环节的零、部件都称为（）。

A．原料

B．外购件

C．在制品

D．半成品

后手