Complete the following statements with proper words or expressio

Complete the following statements with proper words or expressions according to the course book.The characteristic of idioms — ( ) unity can be reflected by the understanding of such idiom as "rain cats and dogs".
【正确答案】：SEMANTIC
【题目解析】：习语的特征——语义的整体性反映在某些习语的理解上面，例如："rain cats and dogs"（倾盆大雨）此类。