Unlike free phrases, the structure of an idiom is to a large extent( ), as is show in
the idiom"in a brown study", which cannot be changed into"in a brown hall”.
【正确答案】：UNCHANGEABLE
【题目解析】：本题考查习语结构的稳定性。Unlike free phrases, the structure of an idiom is to a large extent unchangeable. however as an idiom to mean "deep in thought", the structure is fixed.与自由短语不同，一个习语的结构在很大程度上是不可改变的。比如in a brown study作为"沉思"，这个习语出现时，它的结构是固定的。
