Answer:
The correct answer is option c. "a pressure for darker or lighter skin, depending on the intensity of UV in a geographical region".
Step-by-step explanation:
Humans exposure to ultraviolet light have both, beneficial and harmful effects. In consequence, human skin pigmentation have adaptated to receive different levels of ultraviolet light by synthesizing different levels of melanin (a pigment that protects skin to ultraviolet light) depending on the intensity of UV in a geographical region. This process have been occuring during human evolution history, and it explains why human pigmentation differs among human races.