百思不得其解

.嵿峜繌嗲﹖

#include<iostream>
using namespace std;

class B1{
public:
    B1(int i){
        cout<<"constructing B1:"<<i<<endl;
    }
};

class B2{
public:
    B2(int i){
        cout<<"constructint B2:"<<i<<endl;
    }
};

class B3{
public:
    B3(){
        cout<<"constructing B3:@"<<endl;
    }
};

class C:public B1,public B2,public B3{
    B1 member1;
    B2 member2;
    B3 member3;
public:
    C(int a,int b,int c,int d):B2(b),member2(d),B1(a),member1(c){}
};

int main(int argc,char* argv[]){
    C c(1,2,3,4);
    system("pause");
    return 0;
}

请指教本程序的详细运行过程。谢谢！