Hi mN2,
I read answer choice (C) a little differently.
Let's assume that Moore has a really tiny plumbing business that consists of just one employee: Moore. Let's further assume that in the last year, Moore made 20 house calls. Of those calls, 10 resulted in complaints. Even though this is a small business with a small number of calls, the fact that half of his customers complained could be enough to indicate that he's not a good plumber! Therefore, I don't think that the size of Moore's business would be relevant in determining whether Moore is a good plumber or not.
By contrast, answer choice (B) gives us a little more to work with. The argument in the stimulus is that every complaint filed about poor plumbing in a small town was filed against Moore, therefore he must be a bad plumber since he is single-handedly generating all the complaints. This might be a good argument if Moore worked in a large city with 1,000 plumbers -- if he is that much of a stand-out in such a large field to generate
all the complaints while his 999 competitors generate no complaints, we could safely conclude that he's doing something wrong! By contrast, if Moore is the
only plumber in town it doesn't mean much that he's generated all of the complaints. In this second scenario, we have nothing to compare Moore to. If there were just one complaint against him in a year, he would still have generated
all the complaints. That's not enough, by itself, to conclude that Moore is bad at his job.
I hope this helps clarify things. Good luck studying!
Athena Dalton