C．unique D．social
解析：选D由下文的“we welcome interactions with others”可知，我们是“群居的(social)”动物。
17．A．meeting B．experiment
C．argument D．conversation
解析：选D本文主要讲和陌生人说话，故此处作者是建议读者设想一个陌生人主动和自己“谈话(conversation)”的场景。
18．A．listen B．connect
C．react D．devote
解析：选C当陌生人主动和你说话时，你通常会如何“回应(react)”呢？
19．A．hurt B．forget
C．meet D．benefit
解析：选C你永远不知道通过和陌生人说话你会“认识(meet)”怎样的人。
20．A．happens B．depends
C．affects D．fails
解析：选A站在你身后的人某一天可能会成为你最好的朋友，这样的事情可能会“发生(happens)”。
Ⅳ．语法填空
Tom：Have you heard the news?
Mary：No, what's up?
Tom：I just 1．________ (hear) that our company is planning to lay off 20 percent of the employees in the next two months．
Mary：Are you kidding? I knew they were looking 2．________ some way to cut costs with the lower profits this quarter, 3．________ I didn't think that they would start 4．________ (lay) people off．That is not 5．________ wise choice．The employees will panic when they hear the 6．________．
Tom：Yeah, it's hard to believe．There'll be hundreds of people 7．________ (lose) their jobs．It's not just the salary．It means losing benefits, too．You know, I hope it's not going to be Mike．With three kids and a wife who's sick, that would 8．________ (real) be a blow．Mary：When will we know who is getting 9．________ (fire)?
Tom：I have 10．________ idea at present．If I get any warning, or hear anything else, I'll let you know as soon as possible．
Mary：Thanks．I'll do the same．
语篇解读：Tom听到公司要裁员的消息后，和Mary在谈论此事。
1．heard考查时态。根据语境以及just可判断，此处用一般过去时heard。
2．for考查介词。look for是固定搭配，意思是“寻找”。
3．but考查连词。此处前后语意存在转折关系，故用but。
4．laying/to lay考查非谓语动词。start doing/to do sth．“开始做某事”。
5．a考查冠词。choice是可数名词，故用不定冠词a。
6．news考查名词。根据语境可知，此处指的是前面提到的news。
7．losing考查非谓语动词。此处用v．-ing形式losing作后置定语，修饰people。
8．really考查词性转换。此处用副词really修饰谓语动词。
9．fired考查非谓语动词。get fired意思是“被解雇”，此处get是系动词。
10．no考查副词。此处意思是“我目前并不知道”，故用no。
Ⅴ．短文改错
Dear Sir，
I'm grateful to your good service during my stay in Hong Kong．I'm writing to ask if you could find and send back my bag I left in your hotel．
I checked in on July 1 and out on July 8．Set off in a rush for the airport, I left a bag in Room 713．It's a blue leather bag, what contains some traveling books, a white iPod and some