During the process of ecological succession
a) many new species of organisms evolve rapidly.
b) the number of species in the community decreases.
c) the amount of biomass in the community stays constant.
d) an increasing number of resources and niches become available for animals.

D) An increasing number of resources and niches become available for animals.

This is the answer because, by definition of ecological succession, ecosystems are constantly changing a developing over time.

B says the community is decreasing, which is incorrect, seeing as the development of ecosystems doesn't mean they are decreasing in species. 
A says they evolve rapidly, but evolution can take a while for many species.