for,since,before,after后接时间的区别这四个词分别接时间不一样么?能详说么?

谈since,for,ever,already,yet,just,before的用法? 用before,ever,never,already,yet,since,for填空 for yet ago before since分别用于什么时态 Tom has lived in Shanghai____three years ago.A for B.since C.before D./ I‘ll wait for you _____ you returnA.until B.before C.after D.since Bruce has lived here ( )last year.A./ B.for C.before D.since It all happened a long time ____.A,before B,ago C,for D,since It has been snowing ____several days.A .since B.for C.in D.before it's six weeks__I met you last.a when b.since c.before d.for My father has been a computer engineer____1995a.in b.before c.for d.since I have known him （ ）two years ago1.since 2.for 3.before 4.when Since China will be the host for the 2008 Olympics next year,English is_____useful than before. it's six weeks__I met you last.a when b.since c.before d.for 21.my sister has been studying for a test____a week.A.in B.since C.before D.for 可以说since many years before AFT是什么意思 英语翻译1.Vent Grills for Aft Director Tower 2.Vent Grills for Aft Funnel Trunking 3.Foc's'le Vent Box Grills & Flaps4.Annemometer Fittings The work has lived here for twenty years_____ A,since twenty years ago B.since he came hereC.twenty years ago D.twenty years before 为啥啊