This is a highly chemically modified carbonate. They usually form cave structures.

• A. Dolostone
• B. Karst
• C. Limestone
• D. Calcite

Answer: (B)

The main idea is that caves form through chemical weathering of carbonate rocks by acidic water, a process known as karst. Karst describes both the dissolution-driven alteration of carbonate rocks and the resulting landscape featuring caves, sinkholes, and underground drainage. The clue points to a highly chemically modified carbonate that leads to cave structures, which fits the karst concept best because it encompasses the chemical change and the cave-forming landscape. Dolostone and limestone are carbonate rocks involved in karst, and calcite is a carbonate mineral, but they don’t name the landscape/process responsible for cave formation as neatly as karst does.