Final answer:
The microvilli of specialized epithelial cells are composed of a plasma membrane that covers an actin bundle, with microfilaments supporting the structure, thereby increasing absorption surface area. The correct option is C.
Step-by-step explanation:
The microvilli of specialized epithelia are structurally composed of plasma membrane covering an actin bundle. Inside each microvillus of the epithelial cells lining the small intestine are microfilaments that support its structure. The plasma membrane is folded into these fingerlike projections, significantly increasing the surface area available for absorption.
The dense array of microvilli on the apical surfaces of these cells is often referred to as the brush border. Enzymes fixed to the surfaces of the microvilli help in the final digestion of carbohydrates and proteins.
The vast number of microvilli, estimated to be around 200 million per square millimeter, amplify the efficiency of nutritional absorption from digested food in the small intestine. The correct option is C.