单选题
Regrettably, ______ who don"t have valid identification cards are not allowed to enter the company head office for security reasons.
【正确答案】
B
【答案解析】[解析] 语法：代词
1．这是一道词汇题，选项均为代词。
2．those是由those people who省略people转变而来的。
3．代词those有those who/分词/介词等形式。Those people who are involved in=those involved in