The idiom "diamond cut diamond" is grammatically incorrect, for normally the verb "cut" should take the third person singular "-s". 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
