Final answer:
The nurse should tell the UAP to assess the oral cavity each time mouth care is given and record observations.
Step-by-step explanation:
The nurse should tell the UAP to incorporate technique A, which is to assess the oral cavity each time mouth care is given and record observations, into the client's daily care. This is important because it allows for the early detection of any abnormalities or changes in the oral cavity. It also helps in monitoring the client's oral health status and provides an opportunity for intervention or referral if needed. Techniques B, C, and D are not appropriate for clients who cannot perform oral hygiene tasks for themselves.