Which of the following is one of the characteristics of idioms?（

Which of the following is one of the characteristics of idioms?（ ）
A、Semantic unity.
B、Lexical manipulation.
C、Phonetic unity.
D、Structural variation.
【正确答案】：A
【题目解析】：idioms有两个特征：semantic unity 和structural stability。A选项符合