Hair turns color when we age because the follicles at the base of the hair shaft cease to produce melanin. Melanin is a chemical that gives the hair shaft its color (black, brown, blond, red, and all shades in between). The darkness or lightness of your hair depends on how much melanin each strand contains. With age, the cells in the follicle that produce melanin die off. As they do so, that hair strand will become silver, grey, or white, as it grows.
a. Argument; conclusion: The follicles ... cease to produce melanin.
b. Argument; conclusion: Hair turns color when we age.
c. Argument; conclusion: With age, the cells in the follicle ... die off.
d. Nonargument.
e. Argument; conclusion: The darkness or lightness ... each strand contains.