下列哪种结构不由微管构成（）
A.纤毛
B.纺锤体
C.鞭毛
D.染色体
E.中心体
参考答案：D
If you want to talk to your teacher,you should _____ first.[ ]
A. called to her
B. called up her
C. call her up
D. called her up
试述铅毒作用的分子机理。
