It's two years since he left his hometown.since 为什么不能换成after

It's two years since he left his hometown.since 为什么不能换成after 书上说since不与瞬间动词连用,那it's 2 years since he left his hometown为什么 It's 5 yeas since he left his hometown.意思? it __ about fifteen years since he __ his hometown 改错：it"s 5 yeas since he has left his hometown. It _（be) two years since he left school. It`s two years since he left Shenzhen 改写同意句 It -------- five years since he left his motherland. he left his hometown two years ago Twenty years has passed since he left his hometown.如何翻译? It __ten years since he left Shanghai. It was ten years since I left my hometown.改错