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;
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return 0;
}
- A. mask = mask | READ; mask = mask | WRITE; mask = mask & (~READ); mask = mask | DELETE_;
- B. mask = mask & READ; mask = mask & WRITE; mask = mask | (~READ); mask = mask & DELETE_;
- C. mask = mask | READ; mask = mask & WRITE; mask = mask & (~READ); mask = mask | DELETE_;
- D. mask = mask | READ; mask = mask | WRITE; mask = mask | (~READ); mask = mask | DELETE_;
正确答案：A