— Daddy, will you come home for supper with us today?
— _________, but I might be a little late.
A:I'm busy
B:No problem
C:It's a pity
D:It's hard to say
﹣a3•(﹣a)2的运算结果是( )
神经细胞动作电位形成和恢复的过程中,膜电位变化的次序是
下列有关胚胎工程的叙述错误的是( )