Answer;
B. Periodic drought causes an abrupt decrease in vegetation.
Step-by-step explanation;
-Density-independent factors are those factors limiting the size of a population whose effect is not dependent on the number of individuals in the population, such as weather and climate, exert their influences on population size regardless of the population's density.
-The density dependent factors on the other hand are factors whose effects on the size or growth of the population vary with the population density. There are many types of density dependent limiting factors such as; availability of food, predation, disease, and migration.