Fact 1: Many corals secrete an exoskeleton that builds up to become a coral reef. Fact 2: An atoll is the third type of reef. Given the two facts above, how are atolls built?
Select from the following.
a). important habitats
b). By coral exoskeletons
c). by fish
d). with machines
e). by a type of eel
f). It used to be covered by water
g). The area was once underwater
h). reusing materials
Answer:
b).