This class represents an answer or a response to a question on the Health-Related Social Needs (HRSN) Screening Tool Assessment Instrument. This abstract class exists primarily to re-define the generic AssessmentEvent.responseItem.answer property to the HRSN.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 twenty-six HRSN questions. Note that because this class is abstract, implementers would likely not instantiate this class, but rather the twenty-six concrete sub classes.