多选题

下列程序编译时会出现错误，请根据行号选择错误位置( )

Question

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
}

A. 1,2

B. 2,5,7

C. 3,4,7

D. 4,5,6