Final answer:
A nurse's use of assertive behavior is when they are open and direct when asked by the nurse manager to complete assignments.
Step-by-step explanation:
Assertive behavior is a communication style that involves expressing one's thoughts, feelings, and needs in a direct and respectful manner. In the context of a nurse's use of assertive behavior, option 4, "When a nurse is open and direct when asked by the nurse manager to complete assignments," best describes it. This means that a nurse who is assertive will clearly communicate their availability, progress, and any concerns or difficulties they may have when completing assignments assigned by their nurse manager.