A1 is fouled in the act of shooting just prior to the horn sounding to signal the end of the quarter.
It is impossible to say based on simply this one sentence whether the horn sounded or not. The only thing that is certain is that the foul occurred before the horn. Wording like this is certainly not unheard of on test questions.
If one really wants to split hairs, (who would do that?
) one could point out that even if the horn did sound in the OP, and even if time is not put back on the clock, in this particular case the horn does not end the quarter.