Let's define what "post-apocalyptic" means:
Post-apocalyptic refers to a massive catastrophe that has occurred. The root "post" means after and apocalyptic would mean some terrible disaster. Recall that in an apocalypse, majority of species have been wiped out.
Let's take this into context of the problem:
If post-apocalyptic means desolate wastelands, that would mean that there aren't many organisms left in the world. Resource piles would be depleted, but there are fewer organisms that require it since the population got wiped out. That means there is less competition for resources.
Therefore, our answer is A.