Final answer:
The true statement about the digestive system is that the absorption of nutrients primarily occurs in the small intestine, where villi absorb digested molecules of carbohydrates, proteins, and lipids.
Step-by-step explanation:
When considering the statements about the digestive system, the true statement is that absorption of nutrients occurs in the small intestine. This is where digested food molecules, including carbohydrates, proteins, and lipids, are absorbed by villi. Although digestion begins in the mouth and the stomach plays a significant role in breaking down food, it is the small intestine that is the main site for nutrient absorption. The large intestine is primarily involved in water absorption and the formation of feces, not in the secretion of digestive enzymes or nutrient absorption.
It is also important to note that enzymes such as amylase start the digestion of carbohydrates in the mouth, while proteins are primarily digested in the stomach with the help of enzymes like pepsin. Bile, which emulsifies fats, is released into the small intestine to assist with lipid digestion. Therefore, statement b) 'Absorption of nutrients occurs in the small intestine.' is the correct answer to the student's question.