下列程序的输出结果是 【15】 。#include ＜iostream＞using namespace std;class base { public: int n; base(int x) { n=x;} virtual void set(int m) { n=m; cout＜＜n＜＜’ ’;}};class deriveA :public base { public: deriveA(int x):base(x) {} void set(int m) { n+=m; cout＜＜n＜＜’ ’;}};class derive B: public base { public: derive B(int x):base(x) {} void set(int m) { n+=m; cout＜＜n＜＜’ ’;}};int main(){ derive A, d1(1); derive B, d2(3); base *pbase; pbase=&d1; pbase-＞set(1); pbase=&d2; phase-＞set(2); return 0;}