It ___ 3 years since his grandmather___A is dead B is has dead Cwas dying 请重点解释下第一空

Kitty came here three years ago=It ___ ___ ___ ___ since Kitty __ ___ It ___ six years since I left school.空格填什么?It ___ six years since I left school.能填is,那has been 能不能填啊? it's years since i It's five years since he ___ (come) here说明原因 It has been ten years since I ___(be) a teacher. It ___(be)one and a half years since I __(begin) to study English. her grandmather has been dead for two years同义句it ___ two years since her grandmather __ It has been 3 years since he came here. it is 3 years since Tom has been abroad It ___ 3 years since his grandmather___A is dead B is has dead Cwas dying 请重点解释下第一空 It is said that it ___ here since hundreds of years ago Ahas been existed Bhas existed it is ten years since he became a doctor同义句He became a doctor ___ ___ ___ ___.(4条线) 完成时态和过去时态怎么区分例如下一题 l ___ already (lose) my pen ,l ___(buy)it two days ago____you___(know)him since thenwe ___(be) there many times in the past 3 years. It ___ 6 years since we left middle school.A.was B.had been C.has been D.were It three years since I smoked.翻译 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 1.it is about 600 years ago __ the frist clock was made.(that until when since)2.it was eight'clock ___ he came to school.it was at eight ___ he came to school.(that before since when )