Answer:
B) increased exchange surface provided by their membranes.
Explanation:
The intestine that characterizes by being folded, and by having its walls covered by villi that project into the lumen. They are more concentrated in the first portion of the intestine, decreasing to the final region of the organ. They are involved in nutrients absorption by increasing the absorption area.
Nutrients are absorbed by primary cells and transported to the bloodstream. Mucus is secreted to protect the epithelium during digestion. Villi also transport water from the blood to the intestinal tract, which helps in food decomposition.
Besides the absorption function, the intestine characterizes by doing the peristaltic movement, secretion through special glandules, digestive function, absorptive functions, secretion functions, and endocrine functions.
Animals must have a respiratory membrane to make gas interchange. This surface must be humid, thin, and revested by a simple plane epithelium, plenty of vessels. The membrane must be permeable and exposed for gases to circulate. This membrane might be on the body surface or in specific respiratory organs, such as lugs. The gas exchange occurs by simple diffusion. Oxygen tends to diffuse to the interior of the organisms, while carbon dioxide tends to get out of it.
