单选题
1.设f(x,y)=x+xy,则f(x+y,xy)=( )。
A.x+y+x2y+xy2
B.x+y
C.x2y+xy2
D.2x+2y
正确答案:A
答案解析:f(x+y,xy)=(x+y)+(x+y)(xy)=x+y+x2y+xy2