Final answer:
The nurse's most therapeutic comment would be acknowledging the client's behavior and empathizing with the potential fatigue it may cause.
Step-by-step explanation:
The most therapeutic comment by the nurse would be: I saw you change clothes several times today. That must be very tiring. This statement acknowledges the client's behavior and empathizes with the potential fatigue it may cause. It avoids judgment or criticism, which is important when addressing mental health conditions like obsessive-compulsive disorder.