Which Back Shu point corresponds to the small intestine?

The Back Shu point that corresponds to the small intestine is indeed located at BL-27 (also known as the Back Shu point of the Small Intestine). In Traditional Chinese Medicine (TCM), Back Shu points are associated with the organs they reflect, connecting the organ's functional activity to the physical location of the point on the back.

For the small intestine, BL-27 is specifically designated as the point that influences its function, including digestion, absorption, and the separation of clear from turbid substances. This point is found on the lower back, near the sacral area, and is utilized in acupuncture to address issues related specifically to the small intestine, such as abdominal pain, diarrhea, and other digestive problems.

The other options represent different organs: BL-25 is the Back Shu point of the large intestine, BL-20 corresponds to the spleen, and BL-21 relates to the stomach. Each of these points is critical for their respective organ systems but does not serve to influence or treat small intestine conditions directly. Therefore, BL-27 is the correct answer for its specific association with the small intestine in the context of acupuncture and TCM practices.