45. To be called object-oriented, a programming language must allowAll of the abovefunctions that return only a single valueinclude filesinheritance

The question seems to be a bit jumbled, but it appears to be asking about the characteristics of an object-oriented programming language.

Object-oriented programming (OOP) is a programming paradigm that uses "objects" – data structures consisting of data fields and methods together with their interactions. To be called object-oriented, a programming language generally needs to support the following concepts:

1. Encapsulation: The implementation and state of each object are privately held inside a defined boundary, or class. Other objects do not have access to this class or the authority to change it, except through methods, which are the object's class-defined interface to the outside world.

2. Inheritance: It is a way to form new classes using classes that have already been defined. The new classes, known as derived classes, inherit attributes and behavior of the pre-existing classes, which are referred to as base classes.

3. Polymorphism: This is a concept by which we can perform a single action in different ways. So at a very basic level, you could say that polymorphism is the ability of a message to be displayed in more than one form.

4. Abstraction: It is an extension of encapsulation. It is the process of selecting data from a larger pool to show only the relevant details to the object.

So, to answer your question, an object-oriented programming language must allow inheritance, among other features. It's not about functions that return only a single value or including files.