Could you list the main types of classes in object-oriented programming?

In object-oriented programming (OOP), the main types of classes can be distinguished as follows:

• Regular classes — describe objects with state (fields) and behavior (methods).
• Abstract classes — classes that cannot be instantiated directly, used to define a common interface and basic behavior for subclasses.
• Interfaces — define a set of methods without implementation that must be implemented by classes.
• Static classes — contain only static members and cannot be instantiated.
• Sealed classes — classes that cannot be inherited.
• Nested classes — classes declared within other classes, which can be static or non-static.

In C#, these types help organize code and manage inheritance and polymorphism.