Fact 1: Many corals secrete an exoskeleton that builds up to become a coral reef. Fact 2: Hard corals build by secreting calcium carbonate skeletons. Given the two facts above, what constructs an exoskeleton using calcium carbonate?
Choose from: (1). animals (2). amoeba (3). sharks (4). insects (5). mammals (6). Man (7). coral (8). bats
(7).