A、Immediate action. B、Accurate diagnosis. C、Medical knowledge. D、Expert experience. A文中提到紧急救援的一个原则是“迅速、尽快”，可知答案是A

First aid is the initial care of a suddenly sick or injured person. It is the care administered by a person as soon as possible after an accident or illness. It is this prompt care and attention prior to the arrival of the ambulance that sometimes means the difference between life and death, or between a full or partial recovery.
    The main aims of first aid are:
    To preserve life;
    To protect the casualty from further harm;
    To relieve pain.
    As in most endeavors, the principle to be adopted in first aid is immediate action. Bystanders or relatives not knowing what to do may have unwittingly contributed to unnecessary deaths and chronic injuries. If a person is sick or injured, then he needs help immediately.
    Quick action is necessary to preserve life. A casualty who is not breathing effectively, or is bleeding heavily, requires immediate assistance. If quick effective first aid is provided, then the casualty has a much better chance of a good recovery.
    It is important that quick action does not lead to panic. Careful and deliberate action undertaken without too much delay is most beneficial to the casualty. Try to remain calm and think your actions through. A calm and controlled first aider will give everyone confidence that the event is being handled efficiently and effectively.
    Despite differences between emergencies, you can make it work if you follow the principles of first aid even if you are not sure of what the underlying problem is.