已知数列{an}的前n项和为Sn，且Sn=n2+2n，则a9=（ ） A．20

What’s language for？Some people seem to think it’s for practicing grammar rules（规则） and learning lists of words --the longer the lists, the better. That’s wrong. Language is for the exchange of ideas and information. It’s meaningless if you can’t use it freely. Many students I have met know hundreds of grammar rules, but they can’t speak correctly or fluently(流利地). They are afraid of making mistakes. One shouldn’t be afraid of making mistakes when speaking a foreign language. Native（本土的） speakers make mistakes and break rules, too. Bernard Saw once wrote, “Foreigners often speak English too correctly.” But the mistakes that native speakers make are different from those that Chinese students make. They’re English mistakes in the English language. And if enough native speakers break a rule, it is no longer a rule. What used to be wrong becomes right. So Chinese students should pay attention to grammar, but they shouldn’t overdo(做过头)it. They should put communication(交际)first.

小题1: Language is used to __________ .

A．express oneself

B．practise grammar rules.

C．talk with foreigners only

D．learn lists of words小题2: If too many native speakers break a rule,________ .

A．what they use will become right.

B．they are against the law

C．they should say sorry to others.

D．they will become heroes小题3: When we speak a foreign language, we should________ .

A．speak in Chinese way

B．speak by the rules

C．speak to native speakers

D．not be afraid of making mistakes小题4:What should Chinese students put first?

A．Language

B．Communication

C．Rules

D．Grammar

电气设备漏电可能导致（）引爆。

A.电雷管

B.煤炭

C.岩尘

1Psi等于多少KPa？请计算60Psi等于多少KPa？620.528KPa等于多少Psi？

铁路化学改良细粒土的击实试验，把外掺料加入浸润后的混合料中，应当在1h内完成击实试验的全过程。