贝壳堤由死亡的贝类生物在海岸带堆积而成，在沿海地区经常分布着多条贝壳堤，标志着海岸线位置的变化，下图示意渤海湾沿岸某地区贝壳堤的分布。据此完成下列各题。

Which is the ____ (exciting), football, basketball or volleyball?

Fire is dangerous. What should we do to protect ourselves from the fire? The following is some  16    for you.

How to prepare for a fire?

·Put fire extinguishers(灭火器) in the house. They can help to    17  the fire in a short time. Everyone should know how to use them.

·Fix a smoke alarm(报警器) in the house. It will make a   18    when fire happens. After listening to it, everyone should leave the house quickly.

·Make    19   for escaping (逃脱) from fire. Everyone should know    20 we can escape from quickly. Check the     21    often and see if we can open them easily.

How to escape from the fire?

·  22  open a hot door. It can help fire grow quickly.

·Stay    23 to the floor. The fresher air is near it.

·Roll (打滚) when your clothes burn. 24   is not a good way.

·Never jump off a window. Or you’ll hurt yourself.

If you   25  the fire rules above, you’ll have more chances to live.

()16 A. suggestionsB. plansC. fireD. Water

()17 A. growB. blowC. lightD. Control

()18 A. smokeB. fireC. soundD. Call

()1 A. liftB. plansC. timeD. Floor

()20 A. whereB. howC. whatD. When

()21 A. doorsB. windowsC. desksD. Furniture

()22 A. AlwaysB. UsuallyC. OftenD. Never

()23 A. farB. longC. shortD. Close

()24 A. RunningB. WateringC. RollingD. Covering

()25 A. likeB. breakC. followD. Close

说出下列各个过程中的变量与常量：

（1）我国第一颗人造地球卫星绕地球一周需106分钟，t分钟内卫星绕地球的周数为N，N=$\frac{t}{106}$；

（2）铁的质量m（g）与体积V（cm³）之间有关系式；

（3）矩形的长为2cm，它的面积为S（cm²）与宽a（cm）的关系式是S=2a．

要得到函数$y=\cos \frac{1}{2}x$的图象，只需将函数$y=\sin \frac{1}{2}x$的图象沿x轴(      )