What is the modification of the small intestinal wall that serves to increase surface area?

Villi

Explanation:

Villi are folds on the small intestine lining that increase the surface area to facilitate the absorption of nutrients.

From the experiment it can be concluded that a material or object which has a density that is lesser than water floats. Also, the object that has a density greater than that of water will sink. This is because density is the measure of the amount of substance that is occupied by an object in a given volume.