Jack's made few mistakes in his exam, ______?
A:hasn't he
B:has he
C:isn't he
D:is he
一个施工队要安装一条长805米的管道,已知4天共安装140米.照这样计算,安装完这条管道一共需要几天?
如图表示细胞周期,下列叙述不正确的是( )