Final answer:
The optimal feedback method is to ask non-confrontationally about the situation, focusing on understanding and preventing future occurrences, rather than using accusatory language.
Therefore, option C is correct.
Step-by-step explanation:
The best way for a nurse to give feedback to a nursing assistant who did not take vital signs is option c: The vital signs were not taken. What happened? This approach is non-confrontational and opens the door for the nursing assistant to explain the situation. It allows for a constructive conversation where the nurse can understand potential issues and find ways to prevent similar occurrences in the future. Options a and b are accusatory and can create a defensive environment, and option d diverts from the current issue and can be misinterpreted as questioning the nursing assistant's training rather than the current oversight.