Smith doesn't attack anyone's motives. He doesn't say, for example, that the people who claim meat is unhealthy are biased or have an agenda.

Smith's evidence refers to "most doctors," which doesn't suggest a small or atypical sample. The problem with the argument isn't the representativeness of the doctors Smith is pointing to. It's what Smith infers from their behavior.

Circular reasoning would mean Smith is assuming "meat is healthy" as part of his support for the conclusion that meat is healthy. But that's not what's happening. Smith's support is about what doctors do (they eat meat) and what doctors know (more about health than others). Those are distinct claims from the conclusion, even if the reasoning connecting them to the conclusion is flawed.

This is a tempting wrong answer. Smith does appeal to the authority of doctors, so the first part of (D) might seem right. But look at the second part: (D) says the flaw is that "different authorities give conflicting advice about an issue." There's nothing in the stimulus suggesting that doctors disagree with each other about whether meat is healthy.

This captures what we could anticipate. Smith's argument depends on the assumption that because doctors know more about health, their choice to eat meat reflects their expert judgment that meat is healthy. But (E) points out that Smith is taking for granted that experts don't act against their own best interest. Doctors might very well eat meat despite knowing it's not the healthiest choice, just as a financial advisor might carry credit card debt or a dentist might skip flossing. If doctors eat meat for reasons other than their medical expertise (taste, convenience, cultural habits), then the fact that they eat meat tells us nothing about whether meat is healthy.