He has _______ people visiting him at his house because he fears it will cause…

In sentence-completion (vocabulary-in-context) questions, the correct word must match both the grammatical slot and the exact shade of meaning demanded by the surrounding logic — near-synonyms that differ in degree, intent, or connotation will distort the sentence's meaning even though they fit grammatically.

Here, the clause "because he fears it will cause discomfort to neighbors" tells us the person acted specifically to prevent any visits altogether, not merely to reduce their number. "Stopped" carries exactly this sense of complete cessation, so the sentence reads: he has entirely prevented visitors, motivated by concern for his neighbors' comfort.

Why the other options do not fit:

• "curtailed" means to reduce or cut back partially — it would leave some visits still happening, which contradicts the fear-driven, all-or-nothing tone of the sentence.

• "requested" means to formally ask for something to happen — it reverses the sentence's direction, since the person is acting to prevent visits, not invite or seek them.

• "warned" means to caution someone about a possible danger — it describes giving a caution, not actually preventing the visits from taking place, so it doesn't fit the described outcome.

"Stopped" is the only option that captures the sentence's meaning of completely preventing visits in order to protect the neighbors from discomfort.