This is a 'Complete the Argument' question, where the missing part follows a conclusion word (therefore). The answer choices will hence be conclusions and we have to choose the most logical one, which makes this an Inference question in disguise.

The argument in an Inference question contains only premises that build up to the conclusion - the correct answer choice. This allows me to read the argument without looking for conclusions or assumptions or flaws in the internal reasoning. Calling it into question is simply not required of me - what's required is that I find the conclusion that stems from all this data.

Then I strip down wordiness and style and keep only pure data:

(1) Only happiness is valuable
(2) But we don't like undeserving people to be happy
(3) So allegedly not only happiness is valued, but also the thing that makes people worthy of it
(4) But the thing that makes people worthy of it is how much happiness they bring

Now it becomes clearer what the author is trying to say and what would be her/his conclusion - even deservedness is measured in happiness. The answer choice which most reflects this is C.