单项选择题

下面程序的输出结果是( )。
#include＜iostream＞
#include ＜math.h＞
using namespace std;
class point

private:
double x;
double y;
public:
point(double a, double b)

x=a;
y=b;

friend double distances(point a,point b);
;
double distances(point a,point b)

return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));

int main()

point p1 (1,2);
point p2(5,2);
cout＜＜distances(p1 ,p2)＜＜end1;
return 0;