1.I'm sorry you've missed the train.It__an hour ago.

1.I'm sorry you've missed the train.It__an hour ago.
A.had left B.left
2.She said she ___her mother 3 letters in one month.
A.had written B.wrote
3.His brother ___ a football player since he came to this school.
A.was B.has been C.had been D.is
我想问的是现在完成时和过去完成时的区别.
以及完成时态是不是不能加具体时间,比如:an hour ago这样的.