Which implementation uses both the legacy system and new system until all users verify that the new system functions correctly?

Create a file called favorite_foods, and list your favorite foods, entering five or six or more. press enter after each favorite food so it appears on its own line (make certain you also press enter after the final food item). after the file is created, add two more foods you like that are not on the list (press enter after the final food item). view the list of foods to make certain the two items you added appear at the end of the list