Final answer:
Villi increase the surface area of the small intestine, aiding in the absorption of nutrients.
Step-by-step explanation:
The characteristic that helps increase the surface area of the small intestine is villi. Villi are folds on the small intestine lining that increase the surface area to facilitate the absorption of nutrients. The individual cells on the surface of the villi also have finger-like projections called microvilli, which further increase the surface area for absorption.