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 ofidioms cannot be inverted or changed
C、the meaning of an idiom is to a large extent unchangeable
D、the constituents ofan idiom cannot be deleted or added to
【正确答案】：B
【题目解析】：从题干看，这道题考查的是习语的特点，即习语的结构相对稳定，所以不能交换两个词的顺序。见课本第163页。