Final answer:
In class diagrams, the boxes represent a particular set of objects. These objects contain attributes and methods that define their behavior and properties. The correct answer to the question is 'c. set of objects.'
Step-by-step explanation:
The boxes on a class diagram can be thought of as a particular set of objects. Each box represents a class, and classes are blueprints for objects. Objects exhibit certain behaviors and have properties. A class in terms of Object-Oriented Programming (OOP) defines a set of attributes (which are the data members) and methods (which are the functions or procedures) to define the behaviors of the objects that will be created from the class.
Therefore, the correct answer to the student's question is c. set of objects. It's important to recognize that these objects will ultimately form a set of relationships between one another within the system being modeled.