Chunks of language whose constituent parts never change.

• A. Fixed expression
• B. Idiom
• C. Collocation
• D. Phrase

Answer: (A)

The key idea here is recognizing a fixed expression—a set sequence of words that stays the same in use. These chunks are used as a single unit, and their internal wording doesn’t change; you’re expected to reproduce the exact string as it’s used in common speech or writing. Because the form is rigid, substituting words or rearranging them would break the usual, conventional phrase.

That’s why fixed expressions fit best for the description given. An idiom, while often a fixed form, carries a figurative meaning and isn’t defined strictly by nonchanging parts. Collocations describe common word pairings that can sometimes vary (you can swap related words or change tense), and a phrase is a broad category that can include both fixed and flexible sequences.