Which of the following best describes the relationship between a class and its member functions?

The correct choice highlights the fundamental role that member functions play within a class in object-oriented programming, particularly in C++. Member functions are integral to defining the behavior and characteristics of a class because they encapsulate the actions that objects of the class can perform. When a member function is defined within a class, it can access and manipulate the data members of the class, thus shaping how instances of the class interact with that data.

Member functions can also define operations that the class's objects can conduct, allowing for a clear and structured approach to programming. This means that when you create a class, you typically envision how you'd like to interact with the data it holds, and member functions are the tools that facilitate those interactions, allowing the object to perform its designated tasks effectively.

In contrast, while a class can technically exist without member functions, this situation is rarely practical because it would lack behaviors and functionalities. Furthermore, while it is true that member functions are optional in a class definition, this does not capture their essential role in providing meaningful interactions with class objects. As for the statement that member functions can only modify static data members, this is misleading because member functions can interact with both static and non-static data members, making it an incomplete representation of their capabilities.