Which of the several aspects of the Command pattern may be varied or elaborated to help achieve particular design goals
(a) An invoker may accept registration of more than one command
(b) The invoker may offer operations for un-registering one or more commands
(c) An invoker may offer several kinds of registrations for different kinds of events
(d) All of the mentioned
I got this question in a national level competition.
This question is from The Prototype Pattern, Reactor Pattern and Command Pattern in section Visibility, Accessibility and Information Hiding of Software Architecture