The idiom diamond cut diamond is grammatically incorrect, for normally the verb cut should take the third person singulars. However, we use it as it is. This shows that____.
A、many idioms are grammatically unanalysable
B、the word order of idioms cannot be inverted or changed
C、the structure of an idiom is to a large extent unchangeable
D、the constituents of an idiom cannot be deleted or added to
【正确答案】：A
