When entering the room of a sedated postoperative client, which assessment requires immediate intervention by the nurse?

A. This requires prompt attention but is not immediately life-threatening. B. This requires attention but does not pose an immediate threat to the client's condition. C. An almost completely full urinary catheter drainage bag requires attention but does not pose an immediate threat to the client's condition. D. Administering oxygen without humidification could lead to mucosal dryness and damage, and should be addressed promptly.