婴儿出生后4周内，称为（） A.新生儿期 B.幼儿期 C.哺乳期 D.青春期 E.儿

（）施工连续、进度加快、工期缩短，专业化程度高，不仅保证质量，而且提高了劳动生产率，资源供应均衡，降低了工程成本。

A．顺序作业法

B．流水作业法

C．平行作业法

D．平行流水作业法

Why do airplanes take longer to fly west than east

It can take five hours to go west-east from New York(NY) to London but seven hours to travel east-west from London to NY. The reason for the difference is an atmospheric phenomenon known as the jet(喷射) stream. The jet stream is a very high altitude wind which always blows from the west to the east across the Atlantic. The planes moving at a constant air speed thus go faster in the west- east direction when they are moving with the wind than in the opposite direction.

2. What would happen if the gravity on Earth was suddenly turned off

Supposing we could magically turn off gravity. Would buildings and other structures (建筑物) float away What happened would depend on how ply the things were attached to the Earth, The Earth is moving at quite a speed, moving at over a thousand miles per hours. If you turn something around your head on a string(细绳) , it goes around in a circle until you let go of the string. Then it flies off in a straight line. ’ Switching off’ gravity would be like letting go of the string. Things not attached to the Earth would fly off in a straight line. People in buildings would suddenly shoot up-wards at a great speed until they hit the ceiling. Most things outside would fly off into space.

Where can we most probably read this text（）

A. In a research paper

B. In a short story

C. In a travel magazine

D. In a student’s book

如图所示，物体的重量是600N，不计动滑轮和绳子的摩擦和滑轮重时，当匀速拉动绳子时，作用在绳子上的拉力F为_________________N。

液压系统由（）组成。

A.动力元件

B.执行元件

C.控制元件

D.电气元件

E.辅助元件

F.工作液

手表：时针 自行车：___________ 正确选项为( )。

A．车轮

B．汽车

C．道路

D．骑