Read the following paragraph and answer the question. Give ONLY the answer, no other words or explanation.

For example:

Answer: <most likely answer, as short as possible>.

Paragraph: 
Bones look tough, shiny, and white because they are covered by a layer called the periosteum . Many bones also contain a soft connective tissue called bone marrow in the pores of the spongy bone. Bone marrow is where blood cells are made.


Question: What layer covers the bones that make them look tough, shiny, and white?
periosteum
The periosteum covers the bones.