Question

those who doubt the effectiveness of this treatment for pain believe something will reduce their pain, they will experience some relief. the national institutes of health says that acupuncture relieves pain and reduces nausea and vomiting, although it is unclear how it works. the few adverse effects reported are due to improperly sterilized needles or improper delivery, making this still a fairly low - risk option. for anyone considering acupuncture, they should first research its effectiveness for their specific condition. summary of statements published by the national institutes of health: after reading the passage about acupuncture, identify which scientific claim explains why some people say acupuncture does not truly relieve pain. it blocks pain channels. it is unclear how it works. it provides only a placebo effect. it is ancient medicine, not modern medicine.

Explanation:

The passage discusses the uncertainty around how acupuncture works, which is a key - point in scientific evaluation. The National Institutes of Health statement about it being unclear how it works is a scientific claim related to the lack of understanding of its mechanism.

Answer:

It is unclear how it works.