阅读理解
American people like to say “Thank you” when others help them or say something kind to them. People of many countries do so, too. It is a very good habit.
You should say “Thank you” when someone passes you the salt on the table, when someone walking in front of you keeps the door open for you, when someone says you have done your work well, or you have bought a nice thing, or your city is very beautiful. “Thank you” is used not only between friends, but also between parents and children, brothers and sisters.
“Excuse me” is another short sentence they use. When you hear someone say so behind you, you know that somebody wants to walk past you without touching(触摸) you. It's not polite(礼貌) to break (打断) others when they are talking. If you want to speak to one of them, say “Excuse me” first, and then begin talking. You should also do so when you begin to cough(咳嗽) or make any noise before others.
Let's learn to say “Thank you” and “Excuse me”.
，试求a的取值范围．
解得﹣1≤a＜
