A depression in the ground due to a cave collapse or acidic water dissolution of limestone is called a sinkhole. The correct option in regards to the given question is option "A". Sinkholes can be found in several places around the world and their depth and diameter varies from 1 to 600 meters. There is no surety that the sinkholes will be formed very slowly, they can form suddenly as well. Sometimes these sinkholes can be very deadly as people find little or no time to run or react to such an incident. Erosion is one of the main reasons that lead to the formation of sinkholes. These erosions are very hard to detect from above the ground.