Which Reflects Density-Independent Population Regulation

Which reflects density-independent population regulation?
I. a winter storm that kills birds with equal probability regardless of bird abundance
II. a drought that kills a higher proportion of plants when there are many plants and a smaller proportion when there are fewer plants
III. a lethal disease that is more easily transmitted when animals are found in high abundance than in low abundance

A) I only
B) II only
C) III only
D) I and III
E) II and III