下列程序编译时会出现错误，请根据行号选择错误位置( )
#include <iostream>
using namespace std;
class A{
int a1;
protected:
int a2;
public:
int a3;
};
class B: public A{
int b1;
protected:
int b2;
public:
int b3;
};
class C:private B{
int c1;
protected:
int c2;
public:
int c3;
};
int main(){
B obb;
C obc;
cout<<obb.a1;//1
cout<<obb.a2;//2
cout<<obb.a3;//3
cout<<obc.b1;//4
cout<<obc.b2;//5
cout<<obc.b3;//6
cout<<obc.c3;//7
return 0;
}
