How are atolls built?
Options:
- (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
Hmmm, let me think. I don't want to be wrong, so I got to be careful.
Many corals secrete an exoskeleton that builds up to become a coral reef. An atoll is the third type of reef. Atolls are built by corals secreting an exoskeleton. The answer: (B).