单项选择题

有如下程序:
#include<iostream.h>
using namespace std;
class Demo

public:
Demo() cout<<"default constructor\n";
Demo(const Demo &X) cont<<"copy constructor\n";

Demo userCode (Demo b)Demo c(b);return c;
int main()

Demo a,d;
cout<<"calling userCode()\n";
d=userCode(

A.;
&n