Answer: B) Employers often require their employees to sign them.
Non-disclosure agreements (abbreviated NDA) are documents in which the person signing said agreement must keep certain information from being spread. For instance, if a company has a policy or formula they wish to keep secret, then they would require the proper employees working with this aspect to sign NDA's keeping the items secret. NDA's also extend to things like doctor-patient confidentiality, attorney-client privilege's, and so on.