Which of the following can NOT be defined as a word?

Which of the following can NOT be defined as a word?
A、man
B、for
C、ment
D、blackmail
【正确答案】：C
【题目解析】：该题考查对词汇和词缀的理解，只有C选项是后缀，其他都是可以独立使用的单词， 所以C项是正确选项。