You are sailing the ocean and come across an atoll. what can you predict about the origin of the atoll?
a) it was along a mid-ocean ridge
b) it started as a fringing reef
c) it was built up from a carbonate platform
d) it started as an eez methane hydrate

b) It started as a fringing reef

Explanation:

When an island (basically a seamount or eroded volcano) that is formed on a caldera and which is surrounded by fringing reefs starts to sink or the sea level starts to rise gradually and engulf it , i.e. when the fringing reefs starts to grow it gradually forms an atoll .

It is basically a coral reef encircling a logoon . Coral starts to grow and build a fringing reef and later this barrier reef forms the atoll , which encircles a lagoon .