Leads to wrong conclusion. (A) is a principle designed to help us prove that an artist shouldn’t assume something about what they’re expressing. But we’re trying to prove that contemporary novels don’t have much social significance. Nothing in the argument relates to what artists should or should not assume about their work.

Leads to wrong conclusion. (B) is designed to help us reach the conclusion that a novelist should avoid sensationalistic spectacles. But the argument doesn’t concern what a novelist should or should not do. It’s about whether contemporary novels have little of social significance. We’re not trying to prove what someone should do.

Close, but (C) doesn’t trigger. According to (C), if a work does NOT engage the moral sensibilities of its audience, then it’s not socially important. But we don’t have enough to say that contemporary novels don’t engage the moral sensibilities of its audience. Although we know that the transgressions commited are included for the purpose of making readers wonder what will happen next, that doesn’t suggest that those transgressions or other events or features of the work don’t engage moral sensibilities of the reader. So (C) doesn’t trigger and therefore doesn’t strengthen the argument.

Leads to wrong conclusion. We’re trying to prove that there’s NOT much of social significance in contemporary novels. (D) is designed to prove that a novel IS socially significant.

(E) asserts that a novel’s social significance is depends on how much it allows readers to enter the internal world of the novelist’s mind. So if it does NOT allow readers to enter the internal world of the novelist’s mind, then it does NOT have social significance. (E) is the missing principle that gets us from the premises to “little of social significance” in the conclusion.