A:is; would have
B:were; would have
C:was; would have had
D:were; would have had
①血缘关系的结合 ②工具简陋粗糙 ③人们头脑简单 ④生活环境险恶
——摘自一位中学生的日记。
在形成精子或卵细胞的分裂过程中,染色体都要____,每对染色体中各有____进入精子或卵细胞。