Final answer:
The nurse should keep the line open with 0.9% sodium chloride until the new bag arrives.
Step-by-step explanation:
When a nurse is caring for a client who is receiving total parenteral nutrition (TPN) and a new bag is not available when the current infusion is nearly completed, the nurse should keep the line open with 0.9% sodium chloride until the new bag arrives (option a). This is done to prevent interruption in the client's nutrition and hydration. Sodium chloride is an isotonic solution that can maintain the client's fluid and electrolyte balance.