考点1表示比较的从属连词what/as

例1 Engines are to machines ______ hearts are to animals. (2006年高考山东卷)

A. asB. thatC. whatD. which

例2_____ I explained on the phone， your request will be considered at the next meeting.

A. WhenB. AfterC. AsD. Since

例3What a table! I’ve never seen such a thing before. It is ________ it is long.

A. half not as wide asB. wide not as half asC. not half as wide asD. as wide as not half

【解析】what用作从属连词，表比较，用于A is to B what C is to D结构中；而as表示原级比较，常用于as…as结构中，程度修饰语应置于第一个as之前，嵌入的形容词或副词使用原级?另外as还表“正如?按照”，引导方式连词。

考点2表示条件的从属连词if /unless/as long as/once

例4 ________ I know the money is safe, I shall not worry about it.

A. Even though B. UnlessC. As long as D. While

例5Small sailboats can easily turn over in the water ____ they are not managed carefully.

A. thoughB. beforeC. untilD. if

例6You will be successful in the interview ____ you have confidence. (2007年高考福建卷)

A. beforeB. onceC. untilD. though

例7I won’t call you， _____ something unexpected happens.(2007年考全国卷)

A. unlessB. whetherC. becauseD. while

【解析】表条件的连词if/unless/as long as/unless在用法上存在一些区别。as long as用法同only if/on condition that，强调某事的发生以另一事件的发生为前提；if为正面条件，可能会产生好的或坏的结果，若某种条件产生坏的结果，此时的if可用as long as替换； unless为反面条件，表示除非，如果不，故在真实条件句中常和if…not换用；once既表时间，又包含条件，译作一旦。

考点3表示让步的从属连词although/when/while

例8 We had to wait half an hour _______ we had already booked a table.

A. sinceB. althoughC. untilD. before

例9______I really don’t like art， I find his work impressive. (2007年高考山东卷)

A. AsB. SinceC. IfD. While

【解析】although/when/while均可表示让步，后两者的用法较为特殊。although/though引导让步连词时不与but和yet连用；而while却表示“部分接受，但并非全部”，或用于“强调两种情况?活动等之间的差距”；when也可表示虽然，尽管，同even if，常置于句末。