Please choose the correct answer to the question: A researcher found shark fossils on top of a mountain. This evidence suggests which of the following about this region?

Answer1: It was once below a waterfall. Answer2: It was once part of a riverbed. Answer3: It was once covered by an ocean. Answer4: It was once near a freshwater lake.

Answer format: answer1/answer2/answer3/answer4
Answer: answer3