Answer the following question given this paragraph: 

As erosion by groundwater continues, the ceiling of a cave may collapse. The rock and soil above it sink into the ground. This forms a sinkhole on the surface. You can see an example of a sinkhole in Figure below . Some sinkholes are big enough to swallow vehicles and buildings.


Q: What is formed when the ceiling of an underground cave collapses?

 Choices:

- hill

- groundwater

- mountain

- sinkhole

A:
sinkhole
