单项选择题

有如下程序:
#include <iostream>
using namespace std;
class Sample
friend long fun(Sample s);
public:
Sample(long

A.x=a; <br> private: <br> long x; <br> ; <br> long fun(Sample s) <br> if(s.x<2)return 1; <br> return s.x*fun(Sample(s.x-1)); <br> <br> int main( ) <br> int sunl=0; <br> for(inti=0;i<6;i++)sum+=fun(Sample(i)); <br> tout<<sum: <br> return 0; <br> <br> 程序的输出结果是A) 120
B.16
C.154
D.34