GMATGWDSC...为什么可以用完成时?
38.GWD17-Q38:
AllYchromosomesinexistencetodayaredescendedfromasingleancestor’swhoisthoughttohavelivedabout140,000yearsago.
A.asingleancestor’swhoisthoughttohavelived
B.asingleancestor’swhowasthoughttolive
C.asingleancestorwhomitisthoughthadlived
D.theYchromosomeofasingleancestorwhoisthoughttohavelived
E.theYchromosomeofasingleancestorwhomitwasthoughthadlived
求解答!(答案是D,为什么不能选B?)