Meat in the diet is healthy, despite what some people say. After all, most doctors do eat meat and who knows more about health than doctors do? Which of the following, if true, most seriously weakens the inference above?

Taking for granted that experts do not act counter to what, according to their expertise, in their best interest argument

Generalizing on the basis of a sample consisting of a typical cases

Assuming at the outset what the argument claims to establish through reasoning

Appealing to authority, even when different authorities give conflicting advice about an issue.