单选题：5-6. 下列程序的输出结果是

5-6. 下列程序的输出结果是 @[A](2)
```c++
#include

int x1 = 30, x2 = 40;
sub(int x, int y) {
x1 = x; x = y; y = x1;
}

int main()
{
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





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


答案：A