A:by; have been issued
B:with; have come into use
C:in; have come out
D:at; have come into being
判断句子正误。
若 a 与 b 互为倒数,那么 a² 与 b² 是否互为倒数?
精子和卵细胞结合形成受精卵是在( ) 中完成的.