This class represents a question on the Short-Form McGill Pain Questionnaire (SF-MPQ) Assessment Instrument. This abstract class exists primarily to re-define the generic AssessmentInstrument.item.question property to the SF-MPQ.item.question. In other words, of all the possible questions on all the possible assessment instruments, we are explicitly identifying the ten SF-MPQ questions. Note that because this class is abstract, implementers would likely not instantiate this class, but rather the ten concrete sub classes.