Final answer:
The nursing assistant's best response is to inform the nurse that they cannot apply the medication without a nurse present.
Step-by-step explanation:
The nursing assistant's best response would be option C: "As a nursing assistant, I can't apply medication without a nurse present in the room."
Applying medication is a task that falls under the scope of a nurse's responsibilities, not that of a nursing assistant. It is important for the nursing assistant to adhere to their role and not perform tasks that they are not trained or authorized to do. In this situation, it is appropriate for the nursing assistant to inform the nurse that they cannot apply the medication without the nurse present.