What is the best way to check if a person is breathing before performing Hands-Only CPR?

What is the best way to check if a person is breathing before performing Hands-Only CPR?

a) Look for chest motion and watch for the person breathing.
b) Pinch the nose closed and see if the person gasps while breathing.
c) Tilt the person’s head and check for gasping or heavy breathing.
d) Use a mirror under the nose to check for condensation from breathing.