蜗牛爬杆．第一天白天前进3米，晚上后退2米；第二天白天前进4米，晚上后退5米；第三天白天前进6米，晚上后退3米．请你将这个过程记录在表中．

假如蜗牛每天白天前进3米，晚上后退2米．那么，从10米深的井底向上爬，几天能爬到地面？

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

用水壶烧水，水开时壶盖被顶开．对这一现象的解释正确的是（  ）