Answer:
a). mucosa.
Step-by-step explanation:
Mucosa is the innermost layer of gastrointestinal tract (GI tract) that release various hormones and digestive enzyme. The mucosa layer is responsible for the absorption of nutrients in small intestine.
This layer contains finger-like projections (known as villi) that increase the surface area of cell membrane. It allows increased intestinal surface area to absorb nutrition. These villi are joined with blood vessels, which transport absorbed nutrients to the circulating blood.
Thus, the correct answer is option (a).