【提一些英语问题It'stwentyyears<>hecametoworkinthisschool.A.thatB.since答案是B,为什没不选A?StephenHawkingstressedtotheinterviewsthathisaccomplishmentswouldcertaintyhavebeenachievedbyothers,<>A.neverhadhe】

　　提一些英语问题It'stwentyyearshecametoworkinthisschool.

　　A.thatB.since答案是B,为什没不选A?

　　StephenHawkingstressedtotheinterviewsthathisaccomplishmentswouldcertaintyhavebeenachievedbyothers,

　　A.neverhadhelivedB.hadheneverlivedC.hehadneverlivedD.neverhadhelived为什么选B?这句话又如何翻译?

　　Littleiknownwhenitookthetripwhereitcouldleadme.为什么用did不用had?

　　Hedidnotteachhimselftopainthewasinhistwenties.

　　这是一道填词题,我写的是before,答案是until,不知可不可以用before?

　　Anideasuddenlyfloatedintotheweepingsailor'smindthathereallyanappetiteforapeacefullife.为什么这道提填had而不是have?