A ______ can be a bound root, a free morpheme, or a derived form

A ______ can be a bound root, a free morpheme, or a derived form itself to which a derivational affix can be added.
A、stem
B、lexicon
C、compound
D、syllable
【正确答案】：A
【题目解析】：A stem can be a bound root, a free morpheme, or a derived form itself to which a derivational affix can be added.