Answer:
The answer is A because it is a resource that takes many many years to make more of and we cannot make it ourselves
Answer:
find the masses of one is three times the mass of the other.
It depends on how much oxygen you're taking in.
Frame of reference refers to something that is not moving with respect to an observer that can be used to detect motion. For the children on the bus, if they use other children riding the bus as their frame of reference, they do not appear to be moving. But if they use objects outside the bus as their frame of reference, they can tell they are moving.