来自马骁的问题
Evidencehasbeenputforwardshowingthatastronautsexposedtolongperiodsofweightlessness_quiteseverely.A.haveaffectedB.hadaffectedC.havebeenaffectedD.hadbeenaffected答案是选c,为什那么不用用had而用have
Evidencehasbeenputforwardshowingthatastronautsexposedtolongperiodsofweightlessness_quiteseverely.
A.haveaffected
B.hadaffected
C.havebeenaffected
D.hadbeenaffected
答案是选c,为什那么不用用had而用have
