To produce the output "Inside the child class," which line of code should be placed in the main block?

In the context of object-oriented programming, particularly in languages like Python, the output "Inside the child class" suggests that the specific action method we're trying to call is defined within a child class (also referred to as a subclass).

The correct answer involves creating an instance of the ChildClass and then invoking the action() method on that instance. This ensures that the method being called is the one defined in the child class itself, thus producing the desired output.

When an instance of ChildClass is instantiated in the main block with r = ChildClass();, it initializes the object r. Calling r.action() then directly references the method from the ChildClass, allowing us to see the output "Inside the child class" as intended.

This approach highlights the key principles of inheritance and method overriding in object-oriented programming, demonstrating how a child class can extend or modify the behavior inherited from its parent class.