Which of the following words is NOT a stem?

Which of the following words is NOT a stem?
A、international
B、nation
C、national
D、internationalists
【正确答案】：D
【题目解析】：词干的定义是可以往上加任何词缀的词的形式。 从四个选项看，只有D不能往上加任何词缀了。答案依据在课本第42-43页上。