Is the Bat a Mammal or a Bird?

You have been given a task to create a Python program that will demonstrate the concept of multiple inheritance and class hierarchy. The program should include four classes:

1. Animal: This is a general class that represents any animal. It has one method: is_animal(), which prints This is an animal.

2. Mammal: This is a specific class that represents mammals and inherits from the Animal class. It has an additional method: is_mammal(), which prints This is a mammal.

3. Bird: This class represents birds and also inherits from the Animal class. It has an additional method: is_bird(), which prints This is a bird.

4. Bat: This class represents a bat, a unique creature that is both a mammal and a bird due to its ability to fly. This class inherits from both Mammal and Bird classes.