The conclusion isn't that the film has succeeded because the criticism is misguided. Rather we are strengthening the argument, which says that the criticism of the comedy as unrealistic is misguided because it is funny and that's the most important thing for a comedy.
Answer choice D would strengthen this argument because the idea is that if a film succeeds within its genre (i.e. a comedy being funny), then it is successful overall and should not be criticized for being unrealistic.
Try to remember what the answer choices are providing. They are not providing a conclusion (in this case, that the film is successful), there are providing an additional premise that would strengthen the argument (if correct) or not strengthen it (if incorrect).
Hope this helps. Please let me know if you have any other questions.