Luther (Principal)and Marcia (Agent)have an Agency Relationship

Luther (principal) and Marcia (agent) have an agency relationship.Under which circumstances will the relationship end "at will."

A) Luther and Marcia agree their agency relationship will last two years.At the end of that time,the agency relationship is terminated.
B) Luther and Marcia made no agreement in advance about the term of the agreement.One afternoon,Marcia is tragically killed in an automobile accident.
C) Luther and Marcia agree their agency relationship will last two years.One year into the relationship,they meet for lunch and decide the relationship isn't working and both agree to end it.
D) Luther and Marcia made no agreement in advance about the term of the agreement.One day,Luther calls Marcia and tells her he no longer wishes her to be his agent.