Answer:
(D) Mineral Deposit
Explanation:
While soil run off in mud slides are common and hurt the coral reef, it is a natural occurring phenomenon recorded over thousands of years. Blast fishing was common in the early 1900s but is no longer a threat as no one uses them anymore, typically only people living near rivers use them in the tropics, but pose no threat to ALL the reefs in the world as they are rarely the source of blast fishing. While global warming might be the second option here as the waters become of Unpredictable temp. and thus killing the coral. Last time i checked, there was no coral that was dying from boiling point hot sea water. so mineral deposit is your answer!
