Modifications to increase the surface area of the small intestine include all of the following except
a. villi
b. circular fluids
c. duodenal glands
d. microvilli

I believe the correct answer is duodenal glands.

The small intestines is the area where absorption of food occurs and in order for a maximum amount of food to be absorbed, the small intestine adapts itself to increase the surface area for food absorption. Villi are structures that are fingerlike and are just but projections of the epithelial layer of the small intestine. The small intestine has very many villi and microvilli so that a lot of nutrients can be absorbed simultaneously as food passes through it during the digestive process. Circular fluids such as blood that passes all through the small intestines via blood vessels pick up as much of the absorbed nutrients by the villi and microvilli as possible. Duodenal glands do not assist in absorption but rather they assist in digestion by producing digestive juices from the pancrease.