单项选择题

有以下程序：#include ＜iostream＞
using namespace std;
class sample private:
int n;
public:
sample()
sample(int m)

n=m;

sample add(sample s1,sample s2)

this-＞n=s1. n+s2.n;
return (*this);

void disp()

cout＜＜"n="＜＜n＜＜end1;

;
int main() sample s1(10),s2(5),s3;
s3.add(s1,s2);
s3.disp();
return 0,

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