7.The most common use of telecommunication satellites，however，has been for transmitting telephone calls.however

　　在本句中做副词用，意思相当于but.但是however和but在用法上是有差异的。however不放在句首或句末时，前后通常都加逗号，而but则不用。请看例句：

　　1）It is not，however， the only answer to the question. （然而，这不是问题的唯一答案。）

　　2）I'd like to go and see the films，however，I don't have the time. （我很想去看电影，但我没时间。）

　　3）However，we still have 10minutes left. （不过，我们还有十分钟。）

　　4）The composition is well written， there is room for improvement， however.

　　5）I am sorry，but I won't be able to come this time. （很报歉，我这次不能来了。）

　　6）He would like to go， but he was busy. （他想去，但他太忙。）

　　7）It's not cheap， but it's really good. （这个不便宜，但的确很好。）

　　8. Telecommunication can make information from around the world available to use quickly and easily， but some people worry that this may be a risk to our privacy.

　　available是一个形容词，意思是“可得到的；可用的；有效的”。

　　1）I am sorry those shoes are not available in your size. （很报歉，那些鞋没你的尺码。）

　　2）If I am not available when you call， leave a message. （你打电话来时如果我不在，请留个言。）

　　3）If the tickets is available， I will go to the concert. （如果能弄到票，我会去听音乐会。）

　　4）The ticket is available on the day of issue only. （此票仅发售当天有效。）

　　9.We can prevent this from happening by carefully controlling the new technology.

　　prevent…from…意思为“阻止…发生”，也可用stop…from…或keep…from.From可被省去。例如：

　　1）They tried every means to prevent the disease （from） spreading. （他们想方设法阻止疾病曼延。）

　　2）Nothing can prevent him （from） going there.（什么也阻止不了他去那儿。）

　　本课主要词组及语法要点

　　词组：

　　1. at the beginning of       2.means of

　　3. over long distance        4. by the middle of

　　5. such as                   6. change into

　　7. from…to…                8. be capable of

　　9. not only…but…           10.in theory

　　11. have access to           12.amount of

　　13. provide…to…            14.follow sb's instructions

　　15. care for                 16. as well as

　　17. at the same time         18. make…available

　　19. pay for                  20.isolate…from…

　　语法：

　　1.过去完成时

　　1）…both radio and television had be come established means of transmitting sounds and pictures.

　　2. 非限定性定语从句

　　1）…radio waves， which are then sent from a station on earth to an orbiting satellite.

　　2）…back to earth， where another station picks them up and changes them back into television signals.

　　3）The combination of satellites，which transmit information，computers，which store information，and television，which displays information，will change every home into an education and entertainment center.

　　2. 宾语从句

　　1）We must remember that technology alone is not the answer.

　　2）The satellite also demonstrated how it could provide help to people living in isolated areas…。

　　3. 注意such as，as well as，as的用法

　　1）In order to transmit an event such as the Olympics via satellite， …

　　2）…printed materials such as books and magazines.

　　3）…as well as get any information they need， …

　　4）As one telecommunication expert days， …

　　Text B  What People Don't Know about Air

　　短语表达

　　1. without

　　We couldn't have finished the work so soon without your help.

　　Without air，there would be no wind or clouds.

　　2. adv. + past participle

　　It is widely known that the earth goes around the sun.

　　It is generally believed that the earth is getting hotter.

　　3. where

　　Where there is a will，there is a way.

　　Where there is hope，there is life.

　　4. be forced to

　　He was forced to drop out of school.

　　They were forced to work 14 hours a day.

　　5. shelter v.& n.

　　Mother tried to shelter her from the blow of the tragic news.

　　You have to find shelter from the blazing sun.

　　6. protect from

　　It is necessary that we protect our skin from being burned by the sun.

　　She had his umbrella to protect her from the sun.

　　7. deadly adj.

　　They made a deadly attack on the enemy's air base.

　　A drop of this poison might be deadly to man.

　　8. burst

　　As he braked a tire burst.

　　All the boys burst from their tents.

　　Everybody in the room burst out laughing.

　　The little girl burst into tears.

　　9. rest upon

　　His arm rested upon the table.

　　The task rested upon my shoulder.

　　His eyes rested upon a strange object.

　　10. gaze at

　　He was standing at the window， gazing at the street.

　　What are you gazing at？

　　11. not…until

　　He didn't go out to play until he finished his homework.

　　No one was to go to bed until further order.

　　12. in the meantime

　　His case won't come to court for several months， and in the meantime more than half of the people think him guilty.

　　At last we were released. In the meantime， our friend had informed the newspaper.

　　13. pay attention to

　　Please pay more attention to your spelling next time.

　　I didn't pay much attention to what he said yesterday.

　　14. add to

　　If you praise others more often， you can add great happiness to their life.

　　What he said just now added to my confusion.