The young man fell in love with the beautiful girl at first sight .

　　He fell in love with her when they worked together in the country .

　　He liked the girl but didn\'t fall in love with her .

　　7 . make sure of + sth . / doing sth . 意为“将……弄确切；确保……”。

　　We should get there as early as possible in order to make sure of getting a ticket for the concert .
　　
　　Will you make sure of his return?
　　
　　make sure + that - clause 还可以作为一个句型掌握。如：

　　I haven\'t made sure that I will win the match .

　　Please make sure that lights are turned off .

　　Will you make sure that he returned?

　　Make sure that you pick me up at five .

　　8 . set fire to sth . ( = set sth . on fire ) 意为“放火烧某物；使某物着火”。例如：

　　The enemy set fire to the village .

　　( = The enemy set the village on fire . )
　　
　　单元难点疑点思路明晰

　　1 . The guards couldn\'t have been watching very carefully . 卫兵不可能一直进行严密的监视。

　　〖 明晰 〗 ( 1 ) 对于现在事件的否定推断，可用 can\'t 或 couldn\'t 加上动词 be 的不定式一般式。如：
　
　　child：Can I have some sweets? I\'m hungry . 我可以吃一点糖果吗?我饿了。

　　Mother：You can\'t / couldn\'t be hungry . You\'ve just had dinner . 你不会饿的，你刚吃过饭。

　　( 2 ) 对于过去事件的否定推断，可以由 can\'t / couldn\'t + 任何动词的不定式完成式来表示。例如中“couldn\'t + have been + v . - ing”是couldn\'t + 不定式的完成进行式，表示“想必不可能一直在进行”的意思。例如：

　　It\'s very late now . Jack can\'t have been waiting at the bus stop .

　　All the lights were out . They couldn\'t have been working in the factory .

　　She couldn\'t have been writing . So far as I know , she has been ill since last month .

　　( 3 ) 在其它时态中的用法。例如：

　　Tom：A man answered the phone . I suppose it was her husband .

　　Ann：It couldn\'t have been her husband . He\'s been dead for ages .

　　Ann：Who brought the grand piano upstairs?

　　Mary：Perhaps it was Tom .

　　Ann：He can\'t / couldn\'t have dome it by himself .

　　2 . You must have been mad to speak to the servant! 你跟那个仆人讲话，准是发疯了!

　　〖 明晰 〗 ( 1 ) “must have + 过去分词”表示对过去情况比较肯定的推测，意为“准是”，“想必一定是”。又如：

　　She must have been very young when she got married .

　　The ground is wet . It must have rained last night .

　　He must have arrived by now .

　　Mary must have caught a cold . she had a high fever last night .

　　( 2 ) 对现在情况的推测，用“must + 动词不定式 ( 不带to ) ”，如：

　　Mary must catch a cold , she has a high fever .

　　This must be your room .

　　Comrade Li must be in the dormitory now .

　　You must be joking .

　　He must be seventy now .

　　3 . She understood what I was talking about , even though it was the first time we had spoken together . 即使这是我们第一次在一起讲话，她也懂得我同她谈的道理。
　
　　〖 明晰 〗 ( 1 ) 在下列表达方式之后，要用完成时：

　　it ( this , that ) is the first ( second , third , fourth… ) time…

　　it ( this , that ) is the only…

　　it ( this , that ) is t he finest ( worst , most interesting ) … 例如：