Answer:
The correct answer is option D) "acidification of the ocean caused by increased atmospheric carbon dioxide emissions that dissolve in water".
Step-by-step explanation:
According to scientific evidence, coral reefs and many organisms that have calcium carbonate shells are affected by high carbon dioxide emissions. When sea water absorbs carbon dioxide, the pH of water is reduced in what is known as acidification of the ocean. In consequence, less calcium carbonate is available for coral reefs to be used as shells, which traduces as a major threat for their populations.