76. 有如下程序：
#include<iostream>
using namespace std;
class base1{
int a1;
public:
base1 (int ba){a1 = ba;}
int geta(){return a1;}
};
class base2{
int a2;
public:
base2 (int ba){a2 = ba;}
int geta(){return a2;}
};
class derived:public base1,public base2{
int b;
public:
derived(int da1,int da2,int db):________{b=db;}
int getb(){return b;}
};
若编译无错，则下划线处缺失的语句是______。
