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;

A．2

B．4

C．8

D．16

典型脊髓半横断综合征（Brown-Sequardsyndrome）最常见于（）

A.脊前动脉闭塞

B.急性脊髓炎

C.脊髓急性硬膜外脓肿

D.脊髓髓外硬膜内肿瘤

E.脊髓空洞症