Why is A correct? Why is D incorrect?

@lsatmax can I also get an explanation for this questions

@Ryan-Mahabir & @Lauren-Au, Answer Choice A is correct because it is supported by lines 16-20 telling us that continuous production of jokes requires that the creators are able to recoup their costs, and since there is no formal legal protection system in place, stand up social norms operative among comedians must substitute for the ip law and allows comedians to recoup their costs. Answer Choice D is incorrect because it is too general, we cannot infer that law-based IP systems "generally" work efficiently than systems based on social norms, the author would likely agree that to be true in the case of jokes and comedic routines, but we have no information to determine the author's opinion on IP law as applied to other industries. Hence, it would be improper to infer that he generally finds social norms more efficient in all cases. Let me know if this makes sense and if you have any further questions.

Why not C?

Or E?