For this particular question, I'm not really sure why answer choice B is correct over answer choice C. In the LSAT, do motives usually apply to reasons relating to self-interest, such as profit-motive? Additionally, aren't presuppositions or assumptions not stated in the stimulus. Maria seemed to be directly attacking Lucien's intermediary conclusion that homelessness is caused by people's unwillingness or inability work.
Comments
However, look carefully at L's actual argument. She says this:
There are some empty apartments that exist (in my building and in my friend's building). Therefore, there are apartments available [this seems actually pretty decent so far]. Since there are apartments available, homelessness is caused by unwillingness to work [This is where the problem exists].
L never actually states whether or not the homeless are working, she just assumes it. M points this out by giving us evidence that directly contradicts that assumption: a lot of homeless are not only willing to work, they actually ARE working. For that reason, answer B correctly describes M's retort.
Answer C is incorrect because M doesn't call out L's motives. M would have needed to say something like "Of course you came to that conclusion. You have a financial interest in seeing people go homeless!." M doesn't do anything like that.