Every Java program consists of which of the following?

Every Java program is fundamentally built around the concept of classes. In Java, a class serves as a blueprint for creating objects, which encapsulate both data and behavior. The class structure allows programmers to define the attributes (variables) and methods (functions) that operate on those attributes, providing a way to model real-world entities and their interactions.

While functions are indeed part of a Java program, they are typically defined within the context of a class as methods. Modules and scripts are terms that relate to different programming paradigms or languages and don't capture the core structural requirement of a Java program. Therefore, class-based programming is essential in Java, making it the correct answer in this context.