The small intestine is the main place for absorption. There are many folds on the inner surface of the small intestine, many folds on the surface of the folds, and many small intestinal villi on the surface of the folds. The villi wall and capillary wall of the small intestine are all composed of a layer of epithelial cells, which shows that the small intestinal villi belong to tissues, not organs.

So the answer is: √.