since引导的主句和从句各用什么时态？

1.since引导时间状语从句时，从句动词通常用一般过去时，主句动词用现在完成时。 We have been good friends since we met in 1980. 2.since从句中，有时也用动词的现在完成时情况，但从句意义就起了变化。 I haven't gone shopping since I was ill. I haven't gone shopping since i have been ill. 3在It is+时间+since…这样的节后中，也可