A Positive Apnea Test Determining Brain Death Is Based On

A positive apnea test determining brain death is based on:

A) PO₂ ?80% while receiving 100% oxygen per ventilator.
B) PCO₂ of 60 while receiving 100% oxygen per ventilator.
C) Lack of effort to breath after discontinuation of mechanical ventilation
D) Lack of cough reflex response to tracheal irritation.