A. It is an isolated, flat-topped underwater volcano mountain
B. It is a cauldron-like volcanic feature formed by the emptying of a magma chamber
C. It is a steep conical hill of loose pyroclastic fragments around a volcanic vent.
D. It is an area of land surrounded by one or more younger lava flows

Solution

C. It is a steep conical hill of loose pyroclastic fragments around a volcanic vent.