3.He told me that he had worked in that factory for more than 3 years.
这个句子中的从句需要过去完成时,因为he told me发生在过去,而“他在那里工作”发生在 he told me之前,所以是“过去的过去”,这里就是 he had worked.
5.I haven't seen you for months.
是指“到现在为止,我有几个月没有见到你了”,所以用现在完成时.而where have you been?是“你去了哪里啦?”
完成时用法：
过去完成时表示“过去的过去”.如：
When he came yesterday,I had finished my homework.（他昨天来的时候,我已经完成了作业.）
有关现在完成时的用法：