Final answer:
The nurse should determine respiratory function as the first action when caring for an unresponsive client.
Step-by-step explanation:
The nurse should take the following action first:
a) Determine respiratory function: True
When a client becomes unresponsive, the nurse's priority should be to assess their respiratory function. This involves checking for signs of breathing, such as chest rise and fall, listening for breath sounds, and assessing oxygen saturation levels. If the client is not breathing, the nurse should initiate appropriate interventions, such as providing artificial ventilation or initiating CPR.