What is the proper way to determine that someone is unresponsive before administering cpr?

When I first learned our instructor told us o try and speak with the person another way to check if their blood is moving as should you can always just use the pink-puple-ish part of your nail and if you press it down and count to three if the color is not back the patient is in need of a responder if not the person is fine though before anything you must always try and get them to answer some questions to see if they understand the situation. Sorry I got carried away

Iwould say a is correct