— I can't understand why my mother always keeps me hard at my work. 

— When you ____ children of your own, you will understand. [ ]

A. will have

B. are having

C. have had

D. have to have

分离流感病毒常用的方法是（）

A、接种到Vero细胞上分离培养

B、接种到Hela细胞上分离培养

C、接种到MDCK细胞上分离培养

D、接种乳鼠分离培养

E、接种鸡胚中分离培养