Final answer:
The color of a person's skin is primarily determined by the amount of melanin present. The more melanin in the skin, the darker it is. One person's skin is darker than another's if it contains A. greater amounts of melanin.
Step-by-step explanation:
The color of a person's skin is primarily determined by the presence of a pigment called melanin.
The more melanin present in the skin, the darker the skin color.
As such, option A, Greater amounts of melanin, is the correct answer to the question of what makes one person's skin darker than another's.
Melanocytes, the cells in the skin that produce melanin, create more of it when stimulated by UV light, resulting in the skin darkening or tanning.
Skin color can vary widely among individuals due to factors such as heredity and exposure to sunlight. Although everyone has roughly the same number of melanocytes, people with darker skin produce more melanin.
It's also important to note that while melanin contributes to the coloration of the skin, other pigments like carotene and hemoglobin play a role, particularly in people with lighter skin tones.