下面的程序是位掩码技术实现权限的组合管理。首先定义四个权限常量，分别对应读、写、修改、删除， 每个权限占用整数的一个独立二进制位。初始化权限掩码 mask 为 0 ，代表没有任何权限。如果想实现如下的操 作：添加读权限；添加写权限；清除读权限，其他位不变；添加删除权限。则横线处应该填入的是（ ）。

#include <iostream>
using namespace  std;

int main() {
    const  int READ  = 1 << 0;
    const  int WRITE  = 1 <<  1;
    const  int MODIFY  = 1 <<  2;
    const  int DELETE_  = 1 <<  3;
    int  mask = 0;
    __________________________
    return  0;
}

{{ select(1) }}

• mask =  mask | READ;
  mask =  mask | WRITE;
  mask =  mask & (~READ);
  mask =  mask | DELETE_;
  

• mask =  mask & READ;
  mask =  mask & WRITE;
  mask =  mask | (~READ);
  mask =  mask & DELETE_;
  

• mask =  mask | READ;
  mask =  mask & WRITE;
  mask =  mask & (~READ);
  mask =  mask | DELETE_;
  

• mask =  mask | READ;
  mask =  mask | WRITE;
  mask =  mask | (~READ);
  mask =  mask | DELETE_;