单选题：下列程序的运行结果是()。

下列程序的运行结果是()。
int x1 = 30, x2 = 40;
sub(int x, int y)
{ x1=x; x=y; y =x1;}
int main(void)
{ int x3 =10, x4=20;
sub(x3, x4);
sub(x2, x1);
printf("%d,%d,%d,%d\n" , x3, x4, x1, x2);
return 0; }



A.10, 20, 40, 40
B.10, 20, 30, 40
C.10, 20, 40, 30
D.20, 10, 30, 40


答案：A