This class represents an answer or a response to a question on the Morse Fall Scale Assessment Instrument. This abstract class exists primarily to re-define the generic AssessmentEvent.responseItem.answer property to the MorseFallScale.responseItem.answer. In other words, of all the possible answers on all the possible kinds of assessment instruments, we are explicitly identifying the possible answers to the six Morse Fall Scale questions. Note that because this class is abstract, implementers would likely not instantiate this class, but rather the six concrete sub classes.