State Machine Events in UML are triggers for transitions and do not classify as objects or classifiers; thus they do not inherently have features:

A.Incorrect, because State Machine Events are not treated as classifiers with features.

B.Incorrect, though it hints at an extended use case, State Machine Events do not extend classifiers in standard UML usage.

C.Correct, State Machine Events are not Classifiers and therefore cannot have features such as properties or operations.

D.Incorrect, because UML State Machines certainly have an Event concept, but these Events are not classified as having features.

References:

UML Specification: State Machine chapter, specifically sections discussing the nature of events and triggers.

Further insights can be found in the event and trigger management sections of the UML 2.5 Documentation.