You are presented with the quiz "the bones of what can be found to signify that place used to be covered by water?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "if fossils of a water animal or plant are found in a place then that place used to be covered by water in the past" and "gastropod Shells of marine animals are often preserved as fossils". 

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


 

        gastropod shells   