In UML, a simple State can indeed be redefined, but the specifics of how it is redefined matter:
* Ais incorrect as redefinition of States, including simple States, is permitted.
* Bis correct. A simple State can be effectively removed or altered through redefinition in a derived StateMachine, which could include changing its type or characteristics.
* Csuggests that a simple State can be turned into a composite State. While theoretically possible in the context of redefinition, this option might be considered a significant alteration that could be misleading without additional context.
* Dis incorrect; UML does support State Redefinition.
References:
* UML Specification, particularly the sections on Redefinition and StateMachines.
* Detailed rules on state redefinition are outlined in the UML 2.5 Documentation, specifically under StateMachine specializations.