A reef is made of
it keeps an organism warm salt and water. granite magnesium gastropod shells ocean water calcium carbonate zinc
A B C D E F G H
Coral is calcium carbonate with a trade of carotene.
calcium carbonate becomes a  reef.
A reef is made of (A) it keeps an organism warm (B) salt and water. (C) granite (D) magnesium (E) gastropod shells (F) ocean water (G) calcium carbonate (H) zinc