Answer:
Make sure everyone meets criteria.
Not taking supplements( As some may contain Vit D)
No tanning beds
make sure no one has a hypoactive response to vitamin d through whatever way. Injection, capsule, spray.
Check for genetic conditions or cancers like melanoma which indirectly affect vitamin d levels
Explanation:
These are some of the main things to look out for
Make an hypothesis
i guesss they have to make an hypothesis first
A large naturally occurring community of floral and fauna occupying a major habitat, e.g. forest or tundra
The answer is the rock cycle