—______ does your school have sports meeting?

—Twice a year.

A．How often

B．How soon

C．How long

D．How far

以下程序段共有错误( )处。
#include ＜iostream＞
using namespaces std;
class Sample

private:
int n;
public:
Sample (int i)

n=i;

void setvalue(int i)

n=i;

void display()

cout＜＜"n="＜＜n＜＜endl ;

;
int main()

const Sample a(10);
a.setvalue(5);
a.display();
return 0;

A．1

B．2

C．3

D．4