现在完成时是动作发生在过去,状态持续到现在或对现在的影响.since表示自从……（后面常接一个一般过去时）.切记现在完成时不能与瞬间动词连用,如可以说You have been in the army since last year.但不能说You have joined the army since last year.
过去完成时即过去的过去,强调对过去的影响.
1.we_____jim since she was a little girl.A.know B.had known c .have known D.knew
强调自从她是小女孩以来（表过去时间）,我们就认识Jim(强调对现在的影响,即现在还认识）
2.理由见上.
3.ABD均为瞬间动词,不能与时间段连用,C正确.