The minimal free unit of meaning is morpheme.
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Prefixes occur at the beginning of a word, and usually do not change the word class of the original word.
A. 对
B. 错
A root is not always a free form.
A. 对
B. 错
A morpheme must convey a lexical meaning.
A. 对
B. 错
Illustrate the difference between root and stem.
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