I was debating between B and C...but I'd go with B. In order to arrive at the conclusion that people who train their dogs are more likely to participate in dog shows than are people who do not train their dogs, we have to consider that a representative sample of people who do not enroll their in obedience training classes in fact train their dogs.


what's the OA?

OA:B

Can you please explain the answer numerically ?

This is not a well-written (or well thought out) question. The stem isn't correct, as the best answer (B) isn't sufficient to make the conclusion true, just (sort of, kind of, if you're feeling generous) necessary. Let's diagram the argument to see what want in our answer choice:

Premise: 10% of American dog owners enroll their dogs in formal obedience classes.
Premise: 20% of these dog owners participate in dog shows.
Conclusion: People who train their dogs are more likely to participate in dog shows.

The conclusion makes a comparison between dog trainers and dog non-trainers (for lack of a better word), but we don't have any statistics on dog non-trainers! The obvious choice would be something that addresses this, but we don't get it - so we'll take anything that improves our statistics. B says that the training percentage holds for the population, a fact that it is helpful, at least, and gives us a sounder basis of comparison. All the other answers are out of scope or trivial.

This can't be an official question: the logic (and phrasing) is shoddy. I'd advise limiting your exposure to questions like this; just do proper questions from the OG (or if you exhaust those, from retired LSATs, which have well-written CR questions very similar to those on the GMAT).