The correct option is D All of the above
Brain death is defined as the irreversible loss of all functions of the brain, including the brainstem. It is an irreversible event i.e the brain cannot function normally again. It is mainly due to the accident, high blood pressure, brain or brain tumours. It is a condition in which the donation of vital organs(kidney, liver etc) most commonly takes place.
So, the correct option is 'All the above'.