There are many different factors, but some are: the amount of natural resources (food, water, etc.), amount of predator/prey, and availability of shelter.
The answer is the endogenous opiate.
The human body naturally produces its own opiates like substances and uses them as neurotransmitters. These substances include endorphins, enkephalins, and dynorphin, often collectively known as endogenous opioids. Endogenous opioids modulate our reactions to painful stimuli.
I believe the correct response is A. The population of secondary consumers would decrease, as now these organisms can't obtain energy through the food they consume which is the primary consumers as there is none and thus the population in higher tropic level dependent on them would decrease. This is the secondary consumer.
