The answer that you are looking for is:
B) invasive species
I just took the test. Hope that helps!
Answer:
In animals, oxygen combines with food in the cells to produce energy for daily activity and then gives off carbon. The carbon combines with oxygen to form carbon dioxide (CO2) and is released back into the atmosphere as a waste product when animals breathe and exhale.
Population size and density are the two most important statistics scientists use to describe and understand populations. A population's size refers to the number of individuals (N) it comprises. Its density is the number of individuals within a given area or volume. These data allow scientists to model the fluctuations of a population over time.
Acid rain, if I understand the question correctly.
