Final answer:
Reflection is not one of the six primary functions of the skin. The skin's functions include protection, sensation, thermoregulation, vitamin D synthesis, and serving as a sensory organ, but not reflection.
Step-by-step explanation:
The question asks which is not one of the six primary functions of the skin. The primary functions of the skin include protection, sensation, thermoregulation, vitamin D synthesis, and acting as a sensory organ. The options given are a) heat regulation, b) sensation, c) absorption, and d) reflection. Among these, reflection is not a primary function of the skin.
The integumentary system does indeed regulate body temperature (a.k.a. thermoregulation or heat regulation), allows for sensation by containing sensory receptors, and performs absorption to some extent, though it's not its primary function. While the skin does reflect some ultraviolet light due to melanin, reflection as a primary function is more associated with surfaces like mirrors or other shiny objects, rather than biological functions of the skin, which is why 'reflection' is the correct answer.