It will be four years ( ) he can join the army .什么状语从句啊?用什么呢

It will be four years ( ) he can join the army .什么状语从句啊?用什么呢 有关状语从句It will be 4 years before he can join the army.为什么只能用b It is ten years since he ____(join) the army it is four years since I joined the army.这里的is,为什么不用was呢? It was ten years ago ___ he joined the army It _____ ten years since he left the army. It _____ ten years since he left the army . 1.It _____ten years since he left the army . He has ______(join) the army for ten years and is now an off 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 ten years ince he left the army 翻译 为什么用is