题目

19．某一生物有四对染色体。假设一个初级精母细胞在产生精细胞的过程中，其中一个次级精母细胞在分裂后期有一对姐妹染色单体移向了同一极，则这个初级精母细胞产生正常精细胞和异常精细胞的比例为     A．1：1         B．1：2           C．1：3          D．0：4 答案：AWe're still at the airport. If it weren't for the delayed flight, we _____ the concert right now. [     ]A. can be enjoyingB. must have enjoyedC. would be enjoying D. should have enjoyed