The rules that govern which affix can be added to what type of s

The rules that govern which affix can be added to what type of stem to form a new word are called ______.
A、morphological rules
B、phonological rules
C、grammatical rules
D、philological rules
【正确答案】：A
【题目解析】：The rules that govern which affix can be added to what type of stem to form a new word are called morphological rules.