1. He must be from Africa, _________ can be seen from his skin.答案:B. as 解释:as确实可以引导方式状语,比如I did the work as my father taught me.但是,这里是定语从句,只不过先行词不是一个名词或者代词,而是整个句子。在非限制性定语从句中,which和as可以引导定语从句修饰整个句子,注意that、where、when、why等都不行。举列子:They did rather badly in the maths exam,which was not what I had expected.句子中,“They did rather badly in the maths exam” 是我所没意料到的。还有就是 as we all know 结构:As we all know, china is a developping country.这里we all know 的内容就是“china is a developping country”这整一句话。补充一下,as引导方式状语时,从句式完整的句子,而引导定语从句时,则从句缺少成分,比如As we all know,缺少的就是know 的宾语,而宾语其实就是主句“china is a developping country”2. I was about to go shopping _________ it began to rain. 答案:C. when 解释:固定句型be about to do ……when……表示正要做某事时,突然另一件发生,这题的意思就是:当我正要去购物的时候突然下雨了。 when在此句做并列连词,类似于and then“就在这时”,引导的是并列句。它并不是从属连词以引导时间状语从句。when此种用法如果用在过去时的并列句中时,前句有三个特点,即:可能使用过去进行时,或过去完成时,或was about to do sth结构,而后句则使用一般过去时。而as是没有这种用法的(as做从属连词引导时间状语从句时,更多强调主从句动作同时进行)。如:I was sleeping when the telephone rang. 我正在睡觉,就在这时电话响了。I had waited for 3 hours when he came at last. 我已经等了3个小时了,就在这时他终于来了。I was about to leave when the door opened. 我正要离开,就在这时门开了。