133 In the absence of a Doctor, how long artificial respiration and heart compression should be continued

A. When the casualty turns pale and start to go cold CPR can be stopped.
B. When the casualty has had fixed and dilated pupils for 15 minutes, you should stop CPR
C. When the casualty shows no response to the CPR after 20 minutes, it is useless to continue
D. Until the heart stops beating or the rescuer is unable to continue because of fatigue