Final answer:
The integumentary system produces melanin, not melatonin, surfactant, or trypsin; thus, the correct answer is option c (melanin).
Step-by-step explanation:
The integumentary system produces melanin, which is responsible for the pigmentation of the skin, hair, and nails. Melanin is produced by cells known as melanocytes and plays a crucial role in protecting the skin from UV radiation. Functions of the integumentary system also include providing a protective covering for the body, allowing for sensation, and helping maintain homeostasis. In contrast, melatonin is produced by the pineal gland, surfactant by lung cells, and trypsin by the pancreas, making option c (melanin) the correct answer to the question.