You are presented with the quiz "What can be formed by carbonic acid in groundwater seeping through rock and dissolving limestone?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "acavern is formed by carbonic acid in groundwater seeping through rock and dissolving limestone" and "underground caves and caverns pose an exciting adventure to many". 

So, what's the best answer to the question?


 

       underground caves    