two hours ago指从现在算起二小时之前。two hours before指从过去某时刻算起二小时之前。本句是从现在算起,所以用ago.
如果原句改为过去完成时,则用before:
She didn't show up. I had waited for her since two hours before.
I have waited for her since A. two hours before B. two hours ago
请问这两者有什么区别吗?有人说before是指在两小时之前,ago是指在两小时前,那么他们是否都适用于这个句子呢?
【答】在这两个选项中, before 和 ago 都是副词。副词 before 前面不能用表示一段时间的定语, 而副词 ago 则可以。所以,答案是 B. two hours ago (两小时前)。 two hours 表示时间段,two hours ago 则表示一个时间点。