It is 3 years since he joined the army 和It has been 3 hours

It is 3 years since he joined the army.为什么用is不用has been 看到一句It is 3 years since he joined the army.和一句It has been th it has been 5 years since he joined the army 是表肯定还是否定呢 求教英语大 It is three years since he joined the army.为什么是用joined而不是用ha 用since的话,本句应该是：It is ten years since he joined the army. It is said _______ he has joined the army. It is 3 years_____he joined the army. He has joined the army for ten years.和 He has been in the ar 15、 It _____ ten years since he left the army .A.is B.has C. It _____ ten years since he left the army . 　A. is B. has C. it is four years since I joined the army.这里的is,为什么不用was呢? It is ten years since he ____(join) the army