The idiom “by twos and threes” cannot be turned into “by threes and twos”. It shows that unlike free phrases, the structure of an idiom is to a large extent ______．
The idiom “by twos and threes” cannot be turned into “by threes and twos”. It shows that unlike free phrases, the structure of an idiom is to a large extent ______． 【正确答案】：unchangeable
