111 Let $x=\{-1,0,1\}, y=\{-2,-1,0,1,2\}$ and for all elements $x, x+f(x)$ are even, then the number of mappings $f$ from $x$ to $y$ is
A. 7
B. 10
C. 12
D. 15
111 C. $x$ and $f(x)$ are both even, or both odd.
$f(0)$ has three values: $-2, 0, 2$. $f(1)$ and $f(-1)$ each have two values. $f$ has a total of $3 \times 2 \times 2$ $=12$.