Answer the following question given this paragraph: 

Sebaceous glands are commonly called oil glands. They produce an oily substance called sebum. Sebum is secreted into hair follicles. Then it makes its way along the hair shaft to the surface of the skin. Sebum waterproofs the hair and skin and helps prevent them from drying out.


Q: What oily substance prevents the hair and skin of living things from drying out?

 Choices:

- pus

- progesterone

- pancreatic enzymes

- sebum

A:
sebum
