It is 3 years since he joined the army 和It has been 3 hours since he left his office.为什么一个用is 一个用had been

it is 3 years since Tom has been abroad It is five years since he smoked 英语翻译It is 3 years since they got marriedIt is 3 years since they married求翻译.为什么都是since可意思完全不一样诶 it is 3 years since he has been a doctor 怎么翻?还有it is 3 years since he was a doctor 怎么翻译1? It is 3 years since he joined the army.为什么用is不用has been it is ...since ..为什么不用完成时it is 100 years since Qinghua university was found. 英语翻译是不是翻译为：it is 3 years since he has smoked. It is years since we meet last time.（纠错） It is three years since she was in the It is ten years since he ____(join) the army It is forty years since he home 改为间单句 it is years since i saw him（追加）it is years since i saw him为什么不说it is years since i has seen him而it was years since i had seen him 却可以 It is 3 years since he joined the army 和It has been 3 hours since he left his office.为什么一个用is 一个用had been It is 3 years since he joined the army 和It has been 3 hours since he left his office.为什么一个用is一个用has been it is two years since I came here还是it has been two years since I came here 求It is three years since he worked in his office.解释下since It ---------five years since he left for beijing1Was 2have been 3is 4 is going to be it's years since i