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
【题目解析】：虽然这句习语从语法上分析是不正确的，但我们依然这样在用，说明了习语的一个特点就是不讲究语法。
