The answer is b. Prop roots.
Mangroves are small trees and shrubs that live in the coastal zone. Mangrove trees must fight rough tides, huge waves, strong winds, and storms. One of adaptation is prop roots. The prop roots grow out the mangrove trunk, branches or other prop roots until they touch the ground. There they develop an underground root system. These roots serve as a support in the conditions characteristic for mangrove.