The job grade definitions establish distinct lines of demarcation among the different levels of work within an occupation. The definitions do not try to describe every work assignment of each position level in the occupation. Rather, based on fact finding and study of selected work situations, the definitions identify and describe those key characteristics of occupations which are significant for distinguishing different levels of work. In the context of the passage, which one of the following could best be substituted for distinct lines of demarcation without significantly changing the author's meaning?a. agreementb. comparisonsc. connectionsd. boundaries