题目

“Was his father very strict with him when he was at school?” “Yes. He had never praised him _______ he became one of the top students in his grade.” A. afterB. unless C. untilD. When 答案：C一个含AaBbCc三对同源染色体的精原细胞，减数分裂形成4个精子，染色体组合可以是 A．AbC、ABc、ABC、abc    　　       B．ABc、ABC、aBC、aBC C．ABC、abc、aBC、Abc 　　　　      D．ABc、abC、ABc、abC