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
