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

Which of the following is one of the characteristics of idioms?
A、Structural variation
B、Lexical manipulation
C、Phonetic unity
D、Semantic unity
【正确答案】：D
【题目解析】：本题考查习语的特点。The characteristics of idioms include semantic unity and structural stability. 选项中只有D符合。