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