Answer: B. Seawall
Seawalls are parallel structures built to prohibit upland erosion and fast flooding. They are designed on a very massive scale using concrete structures placed along a vast stretch of shoreline especially at urban beaches. It prevents passive and active erosion, but is also known according to research to be the cause of loss of ecosystem services as well as the loss of habitat and the drastic reduction in biodiversity. Natural beaches are in other words, better in conservation of the ecosystem when compared to seawall-impacted beaches.