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 operato-(point p1)

point p;
int px=x-p1.x;
int py=y-p1.y;
return point(px,py);
void print()

cout＜＜x＜＜","＜＜y＜＜endl;

;
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

A．10,10


B．20,20
C．10,20


D．30,30