Mr. Roy is affable ______ his neighbours.

Concept: An adjective that describes someone's manner of being friendly or pleasant toward people takes the preposition "to" (or "towards") to introduce the people on the receiving end of that friendliness. "Affable" means easy to talk to and warmly polite, and the standard pattern is "affable to + person."

Application: The sentence describes Mr. Roy's friendly manner directed at the people around him, his neighbours. We need the preposition that links the friendly quality to the people it is shown toward. "Affable to his neighbours" fits this pattern exactly and means he is warm and pleasant toward them.

Contrast with the other prepositions:

• "of" marks possession or material; after an adjective it appears mainly in the "it was ADJECTIVE of someone" pattern that judges one particular act ("that was affable of him"), not in a description of how a person habitually behaves with people, so "affable of his neighbours" does not work here.

• "from" signals a source or separation, the opposite of directing friendliness at someone, so it cannot join "affable" to the people involved.

• "for" indicates purpose or benefit, not the person one behaves pleasantly toward, so "affable for his neighbours" is wrong.

Result: The correct completion is "affable to his neighbours."