Four years()since I ()the army 求分析

Four years()since I ()the army 求分析 ____ four years since I joined the Army. it is four years since I joined the army.这里的is,为什么不用was呢? --four years since I joined the army.A.There was B.There is It is four years since I joined the army.啥意思 It is three years since I joined the army.改成完成时态 I ____four years since I joined the army.A.There was B.There i It has been 5 years since I was away from the army,but now I 1.It is two years ＿I joined the army.A.before B.since C.that It __four years since i joined the army.这里的is,为什么不用was呢? —When（） you （）the army?In 1978.Since I （）17 years old It is ten years since he ____(join) the army