单选题：The output of the following program is ( ).

The output of the following program is ( ). @[C](2)
```
fun(int x, int y, int z)
{z=x*x+y*y; }

main( )
{
int a=31;
fun(5,2,a);
printf("%d",a);
}
```
A. 0
B. 29
C. 31
D. uncertain




A.0
B.29
C.31
D.uncertain


答案：C