有两道时态题,我有点区分不了.

Our teacher _____for 10 years before she came here.

     A.taught B.had taught C.has taught D.had been taught 答案选B

  2.   Our new English teacher, who is said to have moved back to China, _______in America for almost    10 years.

        A lived B. has lived C. was living D.had lived 答案选A

还有好些的题目,都让我有点无法辨别何时该用一般过去式,尤其是什么最后有for ...months/years 时间类型的.麻烦谁能给我仔细讲解一下技巧什么的