Thanks, Luke! I have to admit that I'm still a little uncomfortable with this question- my instinct tells me that the "leading representatives" phrase, tied to the mention of John Field's nocturnes in the passage, would be enough to infer that John Field's nocturnes typify the London Pianoforte School altogether. In the hope of putting my worry to rest, is it fair to say the following?:
1) In order to "infer" something on the LSAT, we have to be able to definitely prove it to be true- it can't just be "likely to be true"
2) The passage at large suggests that it's not clear that there is a definitive "style" of the London Pianoforte School, so answer A should be suspect from the start
Assuming the above are true, I think I can move on from this question feeling solid about its reasoning!
Thanks again for your helpful response!