第1个回答 2012-05-08
当since 解释为“自从”时,用于现在完成时,通常后跟时间,ago 以及一般过去式的句子。例句;China has taken place great changes since 1978. They have gone to Hong Kong since two days ago. It is(has been) twenty years since they moved here.
since 还有另一层意思“既然,由于”,时态视具体情况而定。本回答被提问者采纳