Read the text and choose the correct answer.V. Millions of years ago, water covered much of what is now North America. As creatures and plants in the water died, their remains settled to the bottom of the water and piled up, sometimes many feet thick. These thick piles have been dug up. Some of the piles in Alaska are made of plants that grow only in warm places. In this way we learn that parts of Alaska were warm, millions of years ago.C. The piles are made up of -