Which of the following pictures features an atoll?
В
А
С
А. А

The correct answer is D.
Explanation
The atolls are a geological formation that originated from the collapse of an oceanic volcanic island. Therefore, the atolls have a ring shape since the mouth through which the lava was expelled is exposed above sea level, giving the atoll a circular shape. These formations are generally found in the South Pacific and its characterized by the formation of corals after biological processes. Therefore, the correct answer is D.