我现在感觉D是削弱, a patient's belief in the medical treatment the patient is receiving can release the body's own chemical painkillers, diminish allergic reactions, and promote healing
D用的是一种很平常、很土的削弱方式,他就是在说alternative 有用,而不是题干中的所谓 One of the reasons alternative medicines is free of such side effects is that it does not have any effects at all.
因为如果alternative能使patient产生这种有如此好的效果的belief不就是很好的反驳了原文,也就是the charge against the alternative is weakened.