What explains why populations fluctuate around the carrying capacity?

a) immigration exceeds emigration, creating an increase in population size.
b) birth rates equal death rates as limiting factors affect population sizes.
c) density independent factors play a greater role than density dependent factors. d) mutualistic relationships exceed parasitic relationships, increasing population sizes.

B) Birth rates equal death rates as limiting factors affect population sizes.

Explanation:

just answered it on USA Test prep

"d.) carbon dioxide and hydrogen sulfide"

the cells uses some of the atoms of the glucose molecules to atp molecules. the atoms of the glucose molecules will then be converted into energy which will be eventually stored in atp. the energy produced which are stored in atp are coming from the glucose’s chemical bonds.