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Air is all around us. It is around us as we talk and play. From the moment we were born, We are surrounded(围绕)by air. When we sit down, it is around us. When we go to bed, air is also around us. Wherever we are on the earth, We are surrounded by air. We live in air.

All living things need air, living things can’t live without air. We can go without food or water for a few days, but we can’t live for more than a few minutes without air. We breathe(呼吸)in air. When we are working or running, We need more air. So we breathe faster than usual. When we are asleep, We need less air.

小题1:From the text, we know that on the earth _____

A．there is air everywhere

B．some animals don’t need air

C．plants need more air

D．for a long time people don’t need air小题2:The writer tells us that _____

A．there is less air on the earth than on the moon

B．the earth is covered with air

C．the earth is covered with water

D．there is no air on the earth小题3:Which is the first important thing for people’s lives?

A．Water

B．Air

C．Food

D．Sunlight小题4:Which of the following things needs air?

A．Land

B．A mirror

C．A cat

D．A river小题5:A man needs more air when he _____

A．dies

B．runs fast

C．takes a rest

D．sleeps

如图10所示，利用皮带运输机将物体由地面运送到高出水平地面的C平台上，C平台离地面的竖直高度为5m，已知皮带和物体问的动摩擦因数为0.75，运输机的皮带以2m／s的速度匀速顺时针运动且皮带和轮子之间不打滑（g=l0m/s²，sin37°=0.6）。

（1）假设皮带在运送物体的过程中始终是张紧的。为了将地面上的物体能够运送到平台上，皮带的倾角θ最大不能超过多少?  

（2）皮带运输机架设好之后，皮带与水平面的夹角为θ=30°，现将质量为l kg的小物体轻轻地放在皮带的A处，运送到C处．试求所需要的时间是多少？

如图所示，OB=40A，杠杆平衡时F=______牛．

建筑工程恢复施工时，应当向发证机关报告，中止施工满( )年的工程恢复施工前，建设单位应当报发证机关核验施工许可证。

A．1
B．2
C．3
D．5

负荷持续时间曲线