-Why do you like playing basketball, Vickers?        

-_____________.[ ]

A. I began to do it last year

B. I have no plan

C. Because  it's  very interesting

D. It doesn't matter

合成尿素首步反应的产物是（）

A.鸟氨酸

B.氨基甲酰磷酸

C.瓜氨酸

D.精氨酸

E.天冬氨酸