The idiom​tit for tat​is not to be turned into tat for tit. This

The idiom​tit for tat​is not to be turned into tat for tit. This shows that （ ）.
A、many idioms are grammatically unanalysable
B、the word order of idioms cannot be inverted or changed
C、the meaning of an idiom is to large extent unchangeable
D、the constituents of an idiom cannot be deleted or added to
【正确答案】：B
【题目解析】：一个习语的结构在很大程度上是不可改变的，比如习语的组成成分不可替换，习语的语序不能颠倒或改变。