instruction:
Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
question:
Very low density is the concentration of gas molecules in the mesosphere.
answer:
What is the concentration of gas molecules in the mesosphere?

question:
A diet rich in calcium and vitamin d may reduce the risk of osteoporosis and related bone fractures.
answer:
A diet rich in calcium and what vitamin may reduce the risk of osteoporosis and related bone fractures?

question:
The skeleton supports the body, protects internal organs, produces blood cells, and maintains mineral homeostasis.
answer:
What structure supports the body, protects internal organs, produces blood cells, and maintains mineral homeostasis?