【正确答案】：
ACCORDING TO THE POSITIONS WHICH AFFIXES OCCUPY IN WORDS, AFFIXATIONS FALLS INTO TWO SUBCLASSES: PREFIXATION AND SUFFIXATION.
PREFIXATION IS THE FORMATION OF NEW WORDS BY ADDING PREFIXES TO STEMS. PREFIXES DO NOT GENERALLY CHANGE THE WORD-CLASS OF THE STEM BUT ONLY MODIFY ITS MEANING.
SUFFIXATION IS THE FORMATION OF NEW WORDS BY ADDING SUFFIXES TO STEMS. UNLIKE PREFIXES WHICH PRIMARILY CHANGE THE MEANING OF THE STEM, SUFFIXES HAVE ONLY A SMALL SEMANTIC ROLE, THEIR PRIMARY FUNCTION BEING TO CHANGE THE GRAMMATICAL FUNCTION OF STEMS. IN ORTHER WORDS, THEY MAINLY CHANGE THE WORD CLASS. 
【题目解析】：本题考查词缀分为前缀和后缀的依据。根据词缀在词中出现的位置，可以分为前缀法和后缀法。前缀法是在词干前面加前缀构词的一种方法。前缀一般不改变词干的词类，只对词干的意义作进一步的修饰。后缀法是在词干后面加后缀构词的一种方法。不像前缀主要改变词干的意义，后缀只有很小的语义作用，其主要功能是改变词干的语法功能。换言之，后缀主要改变词干的词类。