When we speak about stability, we refer to the tendency of an ecosystem to maintain the supply of its ecosystem services in the long term, such as food production, carbon sequestration and soil fertility.
The correct option is
C. If a disease spreads through a population that has a lot of genetic
variation, resistant individuals will survive and the population will
recover.
I would say that in this option there is a variation of the population over time (there is a disease that has a negative effect, causing several individuals to die and there is a reduction in the population). But in turn, genetic variability is what allows some adapted individuals to survive and return to the initial number of the population, achieving stability in the ecosystem.