During an Interview with You, a Client Threatens to Beat

During an interview with you, a client threatens to beat up her elderly parent. You believe she is serious. What should you do?

A) Maintain the client's confidentiality and report nothing.
B) Report the threat.
C) You have a duty to warn the parent.
D) Investigate your state's laws if you do not already know what they are, and if required, undertake your duty to warn the appropriate authority