Complete the sentence with the appropriate word. Students should pay…

Concept: English fixes many verbs to one particular noun by convention rather than by pure meaning — these are called collocations. The verb "pay" is fixed with the noun "attention" ("pay attention to"), meaning to direct one's mind, eyes or ears carefully toward something; a different noun that means something similar cannot simply replace "attention" in this verb slot, because the pairing is fixed by usage, not logic.

Applying it: The sentence needs a noun that completes the fixed phrase "pay __________ to" in the sense of listening carefully to the teachers' explanations. "Attention" is exactly the noun this verb is fixed with, giving the standard idiom "pay attention to": "Students should pay attention to the explanations given by the teachers in the classroom."

Comparing the choices:

• "concentration" belongs with a different verb pattern — one "concentrates on" something or works "with concentration" — not "pays concentration to" it.

• "notice" is fixed with the reverse verb: one "takes notice of" something, never "pays notice to" it.

• "focus" is fixed with the preposition "on" ("focus on", "keep focus on"), not with the verb "pay".

Only the option that completes the fixed "pay ... to" phrase fits the sentence, matching how leading dictionaries (Collins, Oxford Learner's, Merriam-Webster) define this collocation.