Final answer:
The appropriate feedback approach is option c, where the nurse asks the nursing assistant about what happened, focusing on the issue and inviting explanation in a non-confrontational manner.
Step-by-step explanation:
When a nurse must give feedback to a nursing assistant that did not take vital signs, it is essential to do so in a manner that is constructive and fosters a learning environment. Among the options provided, the most appropriate way for the nurse to give feedback would be option c, which states: "The patient's vital signs were not taken. What happened?" This approach is non-confrontational, focuses on the issue at hand, and invites the nursing assistant to explain the situation or provide their perspective, which can lead to a constructive dialogue and potentially address any underlining issues that may have led to the oversight.