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 pl ) 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 pl ( 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