The LSAT will do this regularly on principle questions. We're asked to find a principle in the answer choices that justifies the argument above. I think the statements in the stimulus could only be loosely referred to as an argument
As you scan the answer choices, you're looking to conform to either of the two principles advanced in the argument. Answer choice (C) conforms to the second principle about refraining from acting indiscriminately on one's desires. I do have an issue with answer choice (C) in that I don't see the disinclination resulting from an arduous process.
However, answer choice (A) is the next best answer and it's not very good. Answer choice (A) can be eliminated as the stimulus is about the process by which one chooses to avoid an alcoholic beverage. Answer choice (A) is about the context in which the situation occurs and the consequences that it will bring. I think of it this way, the stimulus is about the past, answer choice (A) is about the present and the future.
This question does not feel appropriate for this part of the LR section, but there are many reasons why a question that allows for such a loose reading of text would appear at Q21.
I hope that helps!