Final answer:
The mucosa, comprised of the surface epithelium, is responsible for absorption and secretion in the body's mucous membranes such as those found in the digestive tract; thus, the correct answer is A. Mucosa.
Step-by-step explanation:
The surface epithelium is responsible for various functions including absorption and secretion. Specifically, the mucosa is the layer that consists mainly of the epithelium which has the capacity to secrete enzymes and mucus, and absorb nutrients and water. The mucosa is a mucous membrane lining the body cavities such as the digestive tract, and it is in direct contact with ingested food, thus greatly involved in secretion and absorption processes.
The mucosa's epithelial layer is supported underneath by the lamina propria, which is a layer of connective tissue. Right beneath the mucosa, there is the submucosa, which supports it, but is not responsible for absorption or secretion. The muscularis layer, also known as the muscularis externa, provides movement and support but does not absorb or secrete. On the outside, the serosa is the outermost layer that forms part of the mesentery and encapsulates the alimentary canal but also does not engage in absorption or secretion.
In conclusion, the correct answer to the question is A. Mucosa, as it is the layer of the alimentary canal that allows for absorption and secretion due to its composition of surface epithelium.