有如下程序：
#include ＜iostream＞
using namespace std;
class point int x, y;
public:
point( int vx, int vy )
x = vx;
y = vy;
point ( )
x = 0;
y= 0;
point operator+( point p1 )
point p;
int px = x+ p1.x;
int py = y + p1.y;
return point( px, py );
point operator-( point p1 )
point p;
int px = x -p1.x;
int py = y - p1.y;
return point ( px, py );
void print()
cout＜＜x＜＜" , "＜＜y＜＜end1;
;
int main () point p1(10, 10 ), p2( 20, 20 );
p1 = p1 - p2;
p1.print ();
return 0; 执行后的输出结果是
A．10，10
B．20，20
C．10，20
D．30，30
