Which of the following traits in humans can be affected by environmental factors?

Among the given options, skin color is a human trait that can be affected by environmental factors. Skin color is a polygenic trait that is determined by the interaction between genetic and environmental factors. The amount and type of melanin, a pigment that gives color to the skin, is determined by genetics. However, exposure to sunlight and other environmental factors can also affect the production of melanin in the skin. For example, people living in regions with high levels of ultraviolet radiation tend to have darker skin to protect against the harmful effects of the sun. On the other hand, people living in regions with less sunlight tend to have lighter skin to facilitate the production of vitamin D. Eye color, baldness, and tongue-rolling, however, are traits that are mainly determined by genetic factors and are not significantly influenced by the environment. Eye color is determined by the amount and type of pigments in the iris, which are mainly determined by genetic factors. Baldness, or androgenic alopecia, is a condition that is influenced by genetics and hormone levels. Tongue-rolling, on the other hand, is determined by a single gene and is not influenced by environmental factors. Therefore, among the given options, skin color is a human trait that can be affected by environmental factors.