Wrong flaw. This mistakes a sufficient condition for a necessary condition. A vivid imagination is sufficient for one to find the plot disturbing, but people lacking such a trait may nonetheless feel the same way about it. The stimulus, however, is flawed in that it draws upon a potentially unrepresentative sample.

No flaw. This properly applies a necessary condition. If a vivid imagination is necessary for one to find the plot disturbing, then it follows that those who found it disturbing must have vivid imaginations.

No flaw. This properly applies a sufficient condition. If those who found the plot disturbing have vivid imaginations, then it follows that many of the people must have vivid imaginations since many of them found it disturbing.

This makes a broad conclusion based on a potentially unrepresentative sample. (D) fails to establish how many people read the new novel. The support says that most people who have read the new novel found it disturbing, but the conclusion requires evidence that most people in general would find it disturbing.

Wrong flaw. This improperly expands a “most” relationship about a subgroup in an attempt to draw a conclusion about people in general. We don’t know how many people with vivid imaginations actually read the novel, so we can’t conclude what proportion of them find it disturbing. The stimulus, in contrast, draws a general conclusion from a potentially unrepresentative sample.