Many corals secrete what to form a coral reef?\nOptions:\n- (A) Chlorophyll\n- (B) salt and water.\n- (C) The area was once underwater\n- (D) Chemical energy\n- (E) aqueous solution\n- (F) Organic compounds\n- (G) gastropod shells\n- (H) hard outer covering Let's solve this problem gradually.

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Many corals secrete an exoskeleton that builds up to become a coral reef. An insect has a hard outer covering called an exoskeleton. Many corals secrete a hard outer covering that builds up to become a coral reef. So the final answer is (H).
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