Question

which part of a piece of hair contains hard keratin that gives hair its stiffness?
options: root, bulb, medulla, cortex, i dont know yet

Explanation:

The cortex of hair contains hard keratin, which provides hair with its stiffness. The root is the base, the bulb is the growing part, and the medulla is the inner core (not main for stiffness).

Answer:

D. Cortex