Please choose the correct answer to the question: Scientists dig in a dry area at the bottom of a mountain range. Fossilized shells of freshwater mussels are found in the area. Which is a likely conclusion that scientists will draw based on this evidence?

Answer1: Rivers once flowed through the area. Answer2: Volcanoes were once active in the area. Answer3: The ocean shoreline once reached this area. Answer4: Floods were a common occurrence in this area.

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