—What's the woman in a white hat?

—__________. [ ]

A. She is my teacher

B. She is a cook

C. She is thirty

D. She is a girl

在哺乳动物尿素循环中，尿素由（）产生.

A.鸟氨酸

B.精氨酸

C.瓜氨酸

D.半胱氨酸

E.蛋氨酸