Answer: b. sinkholes and caves
Ground water is a source or reservoir of water that forms beneath the under surface of rocks and soil, when the water from sources like precipitation, river, lakes, agricultural irrigation seeps through the pores. The accumulated water from the pores is a ground water. The upper layers of soil above the groundwater contains carbon and limestone. The water being combined with carbon becomes acidic which erodes limestone this results in formation of sinkholes and caves.
