The correct option is A Winter storms
Density-dependent factors are the one that affects the birth and death rates of population in a density-dependent manner. These are mostly the biotic factors such as predation, competition, parasites etc. For example, low prey density affects the mortality of predator. Among the given options, winter storms affect the population in density independent manner as it can affect the individual organism. For example, winter storm causing the death of a deer regardless of deer population density. So, the correct answer is option A.