Another slightly dodgy question. In international competition, and in most national competitions outside the USA, the quarters are ten minutes each.
In fact the NBA seems to be the exception; realbuzz.com (a website and organisation that aims to get people actively involved in sport) states "The basketball game consists of four quarters of 10 minutes each."
Fair enough, the question did state "professional NBA"; but there's plenty of scope for confusion here, and that makes this a question best avoided (or reworded to allow "forty minutes" as a correct answer).
© Macclesfield Quiz League 2018