Final answer:
The integumentary system consists of the skin, nails, and hair, which protect the body, help maintain homeostasis, and sense the environment. The correct answer to the student's question is 'd. hair.'
Step-by-step explanation:
The Integumentary System
The integumentary system is the body's largest organ system, which includes the skin and its associated structures such as the hair and nails. These components work together to provide a protective covering for the body, sense the environment, and help the body maintain homeostasis. Both the nails and hair contain keratin, which is a tough protein that gives strength to these structures, similar to chitin found in the exoskeleton of arthropods.
Regarding the student's question, the integumentary system includes the skin, nails, oil, sweat glands, and hair. Therefore, the correct answer is 'd. hair.'