Auroras normally occur in the Earth's thermosphere.
Answer:
I believe it is D.
Explanation:
Ecological succession has to do with how the habitat changes over time. So D would make the most sense.
The number of workers for each person receiving Social Security benefits is called the DEPENDENCY RATIO. An increase in the dependency ratio increases the burden on the productive part of the population and has a direct direct impact on financial expenditures on things like <span>social security.</span>
