Which of the following limiting factors would be directly affected by a drought?
a. birth/death rate
b. immigration
c. available niche
d. resource supply

Obviously, out of the choices above, resource supply would be directly affected by a drought. Drought happens when there is a little rain (or no rain at all) in a long span of time. Thus, agricultural sources of food (and other products which needs rain) would be greatly affected.

your question is incomplete

explanation:

an important point to remember about correlation is that while there is a _statistical_ relationship correlation does not equal _causation_

the first answer is: statistical

the second answer is: causation