On which square should Black put his queen in this position: b4,c4,a5,a6 or b6?

On which square should Black put his queen in this position: b4, c4, a5, a6 or b6?

I first visited the prestigious Royal Automobile Club in Pall Mall when I was kindly invited there by Ray Keene, I think during an event in Harringay in 1989. Ray is not a man who is prone to panic, in fact I would regard him as quite sanguine but when he saw my attempts to comply with the dress code a look of alarm crossed his face rather similar to that of someone who had suffered a back rank mate.
Slightly better attired, I was back at the scene of the crime for a unique, enjoyable event with 10 GMs playing simuls against 10 different teams. It was a pretty tight schedule, but I did manage to finish all my matches within the required time. Although with only 50 minutes to finish before the adjudicators sprang into action I suffered some collateral damage against Lee Heard and Matthew Wadsworth in the game shown above. As you can see I managed to select the only immediately losing square from the five possibilities available. I should mention my youthful opponent made very light work of finishing the game.

After Tara had managed to perform an even more impressive simul (inserting myself and Julian Hodgson into black tie whilst we watched the end of the Man United v Man City FA Cup semi-final) we had an excellent dinner proceeded no less excellently by a champagne reception. Bill Harston gave a speech to round off proceedings; he mentioned his quote “Chess doesn’t drive people mad, it keeps mad people sane” which I gave as my favourite saying about chess in my New In Chess questionnaire. Bill had forgotten saying it until he saw it quoted attributed to him recently, which suggests his memory is going the same way as mine!