用秋水仙素处理植物萌发的种子或幼苗可以得到多倍体，秋水仙素的作用原理是[ ]

A．干扰减数分裂的进行

B．抑制纺锤体的形成

C．抑制着丝点的分裂

D．使细胞连续进行染色体复制

All the students _____ by 10:30, but the speaker _____ until 11:00.[ ]

A. return, has turn up

B. has returned, turned up

C. returned, turn up

D. had returned, didn't turn up