若集合A={-1，1}，B={0，2}，则集合{z|z=x+y，x∈A，y∈B}中的元素的个数为[ ]

A．5

B．4

C．3

D．2

It is so difficult a problem that ____ student in this class ____ work it out.

A．any; can't

B．no; can

C．every; can

D．no; can't