Chess

I agree with pkit above; if the answer is C, this is a bad question. Sure, tennis and chess may both be more fun if you play against someone of equal ability. That doesn't mean that it's just as easy to find a suitable chess opponent as it is to find a suitable tennis opponent, and that's the key question here; it may be that all beginning tennis players are roughly equal in ability, or that tennis was already so popular that finding an appropriate opponent is easy. If C told us that it was hard to find a suitable tennis opponent, and yet tennis was still becoming increasingly popular, then C might be a good answer, but as it stands, it doesn't do much to 'undermine' the consortium's opinion, since it doesn't compare tennis and chess on the correct grounds.

Answer A does provide an alternative explanation for the unpopularity of chess - it's expensive. So it's a perfectly good answer.

I'd add that this does seem like one of those poorly constructed prep company questions, and doesn't have much in common with real GMAT CR, so it isn't worth spending time on.