Hi, Melinda -

The language of the doctor's argument is a little convoluted, but it can be paraphrased roughly as "Since some alternative medicines are safe to consume, it should be legal to prescribe them even if there is no real evidence that they help. After all, it's POSSIBLE that they help, and there's no harm in trying them."

Answer A weakens this argument by pointing out that such medicines may cause indirect harm by encouraging a patient or doctor to neglect an effective therapy in favor of a harmless but ineffective alternative. (For example, it is perfectly safe to consume garlic, but a diabetic who tries to use it as an alternative to insulin is very likely to come to harm as a result.)

By contrast, answer B is irrelevant to the doctor's argument, which is based on the alleged harmlessness of the remedies, not on any claims (true or otherwise) of their effectiveness.

Hope this helps. Please post again if you have further questions.

Best,
Lyn