甲氧苄啶是属于（）
A.磺胺类
B.硫氧嘧啶类
C.二氨嘧啶类
D.乙胺嘧啶类
E.抗生素
参考答案：C
"What does he do?" means _____. [ ]
A. Who is he
B. Where is he
C. What is he
D. What is he doing
设z=f(x，y)，满足
，且f(x，0)=x，f(0，y)=y2，则f(x，y)=______．
，且f(x，0)=x，f(0，y)=y2，则f(x，y)=______．