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
