Final answer:
Drought is a density-independent regulator of population growth because it affects a population regardless of its density. Disease, starvation, and parasites are typically density-dependent.
Step-by-step explanation:
The factor most likely to be a density-independent regulator of population growth among the options provided is A) drought. Density-independent factors are typically physical or chemical (abiotic), such as weather events or natural disasters, that affect mortality rates regardless of the population's density.
Drought can cause mortality in a population whether it is sparse or dense, as it is related to environmental conditions rather than the interactions among individuals within a population. On the other hand, disease, starvation, and parasites are often considered density-dependent factors, as their effects on a population can depend on how densely the population is packed.