Question

8. When you study all the growth characteristics of a human population, you are studying its _____.

Answer 1

8. I am pretty sure that the correct answer for the first question (When you study all the growth characteristics of a human population, you are studying its) is D.demography. The reason why I consider it to be correct is that only this term includes such things as a segmentation or statistical breaks which cleanly coincides with the question.
9. What about the next one, population control factors whose effects increase as the size of the population increases are D.density-dependent. The main point which led me to this answer is that  density-dependent factor is sort of limiting factor that depends on the population size. 
I do hope you will find it helpful! Regards.