Let's start by briefly examining the argument. We are told that a contract exists when two parties engage with each other for the reciprocal transfer of benefits. The argument then concludes that when an artist accepts public funds, this artist has created at least an unexpressed contract with the public and that the public can rightly expect to benefit as well.
Right away when reading this, I am wondering why is it the case that just because the artist is accepting funds that the public can rightly expect to benefit. We don't know that the artist offered anything in return and this was "reciprocal".
This is why answer choice B is correct. The situation conforms only partially in that the artist receives benefits from the other party, but we don't know whether this was reciprocated. The argument, nevertheless, concludes that it goes both ways.
Answer choice C is incorrect for a few reasons. Firstly, nothing in the argument was spoken in abstract terms; there were specific parties mentioned and the benefit to the artist was made explicit (public funds). Second, there were no contingencies mentioned. All that was said is that they are right to expect benefit, not that they necessarily will or will not receive it. And lastly, we don't know for a fact that this relationship between an artist and the public needs to be judged on a case-by-case basis.
What I like about going through incorrect answer choices is finding all the reasons why they are incorrect. It only takes one to confidently discount the answer choice and the more you are able to spot, the easier it is to focus your search on the more promising remaining choices.
I hope this helps. Please let me know if you have any other questions.