A woman appears to be choking. She is unable to speak and allows you to assist her. You perform the Heimlich maneuver and are unable to relieve the obstruction. She becomes limp, slumps to the floor. What should you do next?
a) Begin CPR immediately
b) Continue performing abdominal thrusts
c) Check for a pulse and start CPR if necessary
d) Call emergency services (911 or local equivalent)