When classifying jobs, raters may categorize jobs into groups where the jobs are similar in difficulty but are otherwise different. these groups of jobs are called

Job classification is a scheme of classifying a job according to the current responsibilities and duties associated with the job.
The groups of jobs made during the process of classifying jobs in which raters may categorize jobs into groups where the jobs are similar in difficulty but are otherwise different  are called classes.

C; skin, is the answer!