Leads to the wrong conclusion. (A) is designed for us to conclude that doctors should NOT be trained to treat something. But we’re trying to conclude that doctors need more training.

Leads to the wrong conclusion. (B) tells us what’s necessary to make a change in how doctors are trained. That allows us to conclude that there should NOT be a change in how doctors are trained. But we’re trying to prove that there SHOULD be a change. We want doctors to have more training.

(C) concerns the comparative benefit of treating unpreventable illnesses and counseling for preventable illnesses. But we’re trying to prove that doctors should have more training related to a preventable illness. Unpreventable illnesses are irrelevant to the argument.

Leads to the wrong conclusion. (D) allows us to conclude something about where doctors should focus their efforts. But we’re trying to conclude that doctors need more training in something. What doctors should focus on doesn’t imply anything about the need for more training.

Helps get from the premises to the conclusion. We know from a premise that obesity is a cause of preventable illness. We also know that many doctors don’t feel qualified to advise on obesity. It’s reasonable to take this as evidence that many doctors don’t have enough training in treating obesity. If, as (E) says, doctors should get enough training to treat causes of preventable illness, then that supports the claim that doctors should get more training in treating obesity.