Answer:
A) employment references
Step-by-step explanation:
Employment references are basically what your old employers or supervisors thought about your work performance and how good or bad employee you were, i.e. if you were a good team player, you were responsible, efficient, etc.
As a tip, if you think that your boss doesn't like you or your job, then you should never ask him/her to give you an employment reference.
Prospective employers may use employment references to check if what the candidate is saying is true about his old job and the tasks he/she performed there.
Good employment references can help you get a new job, but bad references can make you lose that opportunity.