第21题: [单项选择]Nowadays Internet enables us to know things happen almost at the exact moment ______ . A. which they are happening B. they are happening C. which they happen D. they have happened 参考答案:B 答案解析:定语从句题。moment后接的是省略关系副词when的定语从句。选项[C]和[D]时态不对,这里主要强调事情发生的同时人们就知道了,所以在选项[A]和[B]中进行选择。而如果采用选项[A]中的句式,则