【正确答案】：
PREFIXATION IS THE FORMATION OF NEW WORDS BY ADDING PREFIXES TO STEMS. PREFIXES DON'T GENERALLY CHANGE THE WORD CLASS OF THE STEM; BUT ONLY MODIFY ITS MEANING. FOR EXAMPLE, "OBEY" IS A VERB, WHICH MEANS "TO CARRY OUT THE ORDER" WHILE "DISOBEY" IS ALSO A VERB, WHICH MEANS "NOT TO CARRY OUT THE ORDER". "OBEY" AND "DISOBEY" HAVE THE SAME PART OF SPEECH, BUT DIFFERENT MEANINGS. 
【题目解析】：前缀是通过在词干上添加前缀来形成新词。前缀法一般不会改变词干的词类，它只会修改它的意思。例如，“服从”是个动词，意思是执行命令，而“不服从”也是一个动词，意思是不执行命令。“服从”和“不服从” 词性相同，但含义不同。