Question

during a prolonged period of ______. people may run out of water.
a drought
b rainfall
c well drilling
d dam building

Explanation:

The sentence describes a scenario where people face water scarcity after a long event. Drought is a prolonged period of little to no rainfall, which causes water shortages. Rainfall brings water, well drilling and dam building are methods to access or store water, so they do not lead to running out of water.

Answer:

a. drought