I would say C: Dam
Sea walls and levees stop water from overflowing onto something. Which can we good but has no impact on droughts.
Storm shelters wont impact droughts either. They are men't to protect people from storms.
A Dam on the other hand can contain and keep water in one given place. Which will save water, to be used to prevent future droughts.
Hope this helps!
Brainliest is appreciated if you feel its deserved!