Coral reef destruction is caused of course by climate change, responsible for our warmer oceans. Corals cannot survive if the water temperature is too high. Higher water temperatures is the main reason behind the death of nearly half of the Great Barrier Reef’s corals.
Urban and industrial waste and oil pollution from shipping are poisoning reefs too – some pollutants, such as sewage and runoff from farming increase the level of nitrogen in seawater, causing an overgrowth of algae, which smothers reefs by cutting off their sunlight.
So A, B and C are the correct answers