Which of the following are true for the singleton class?

• A. Singleton classes should be used whenever it is important that only a single instance of a class exist and that that single instance be widely accessible
• B. The Singleton pattern can also be used, with slight modifications, when a limited number of instances greater than one are desired
• C. Access restrictions are usually easy to add by restricting the visibility of either the class or the factory method
• D. All of the mentioned