46. According to the passage, what is TRUE about bleaching?
(A). It is caused by a steady rise of sea temperature.
(B). It is caused by natural deterioration of coral reefs.
(C). It is caused by a dramatic rise of sea temperature, to which coral reefs respond by ejecting the coral polyps.
(D). It is caused by a dramatic rise of sea temperature, to which coral reefs respond by ejecting the algae that co-exist with them.