What Causes Caverns in Limestone

Multiple Choice

What causes caverns in limestone?

A) Hard grains of quartz sand carried in underground streams erode the soft limestone.
B) They form when rocks above collapse into the limestone.
C) Limestone readily dissolves in seawater, so the caverns formed originally at sea level.
D) Groundwater in limestone is somewhat caustic, so over many years, it dissolves limestone.
E) Rainwater dissolves carbon dioxide to make weak carbonic acid that dissolves limestone.