如果细胞开始有丝分裂时染色体数为2n,那么分裂过程中染色体数的变化应是[ ]
A.2n→n→n
B.2n→4n→2n
C.2n→4n→n
D.2n→n→2n
答案:B
They have formed a habit. That is, they celebrate their birthday _____. [ ]
A. annual
B. monthly
C. weekly
D. annually
工作分解结构是一种()树状结构。
A.层次化
B.并列化
C.网络化
D.无序化