单选题：下列哪个代码能够实现x和y值的交换（ ）

下列哪个代码能够实现x和y值的交换（ ）




A.c++
void fun(int a,int b) {
int x = a;
a = b;
b = x;
}
int main() {
int x = 1, y = 2;
fun(x, y);
cout << x << ","<<y << endl;
return 0;
}

B.c++
void fun(int&a,int&b) {
int x = a;
a = b;
b = x;
}
int main() {
int x = 1, y = 2;
fun(x, y);
cout << x << ","<<y << endl;
return 0;
}

C.c++
void fun(int* a,int* b) {
int x = a;
a = b;
b = x;
}
int main() {
int x = 1, y = 2;
fun(x, y);
cout << x << ","<<y << endl;
return 0;
}

D.c++
void fun(const int&a,const int&b) {
int x = a;
a = b;
b = x;
}
int main() {
int x = 1, y = 2;
fun(x, y);
cout << x << ","<<y << endl;
return 0;
}



answer：B