27.① Coral is an animal, a marine polyp that lives in vast colonies. ② Coral reefs are found in tropical waters, between latitudes 30 degrees north and south, in the Western Atlantic, Indian, and Pacific Oceans. ③ Reefs are outcroppings that rise up from the sea floor. ④ While most of the reefs are the remains of dead coral, there must be good percentage of living coral to ensure that the reef will continue to survive. ⑤ The calcium-based skeletons that they secrete build up over time to form vast reefs.
(A) ①③②④⑤
(B) ①⑤③②④
(C) ①②④③⑤
(D) ①②③④⑤

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統計: A(0), B(13), C(2), D(5), E(0) #797128