The prefix in-is changed to im-in improper;ir-in irreconcilable

The prefix in-is changed to im-in improper;ir-in irreconcilable and il-in illegal,which shows that ______。
A、morphemes are abstract units
B、morphs are actual spoken,minimal carriers of meaning
C、allomorphs are phonetically conditioned and thus predictable
D、affixes can be added to other morphemes to create new words
【正确答案】：C
【题目解析】：chapter III ,P39.allomorphs（语素变体）: some morphemes, however, are realized by more than one morph according to their position in a word. Such alternative morphs are known as allomorphs.