The purpose of the passage is to tell the reader

单项选择题

First Aid
First aid is emergency care for a victim of sudden illness or injury until more skillful medical treatment is available. It may save a life or improve certain vital signs including pulse, temperature, a clear airway (气道), and breathing. In minor emergencies, first aid may prevent a victim’s condition from turning worse and provide relief from pain. First aid must be administered as quickly as possible. In the case of the critically injured, a few minutes can make the difference between complete recovery and loss of life.
First-aid measures depend upon a victim’s needs and the provider’s level of knowledge and skill. Knowing what not to do in an emergency is as important as knowing what to do. Improperly moving a person with a neck injury, for example, can lead to permanent spinal (脊柱的) injury and paralysis (瘫痪).
Despite the variety of injuries possible, several principles of first aid apply to all emergencies. The first step is to cal*l for professional medical help. The victim, if conscious, should be reassured that medical aid has been requested, and asked for permission to provide any first aid. Next, assess the scene, asking other people or the injured person’s family or friends about details of the injury or illness, any care that may have already been given, and preexisting conditions such as diabetes (糖尿病) or heart trouble. The victim should be checked for a medical bracelet (手镯) or card that describes special medical conditions. Unless the accident scene becomes unsafe or the victim may suffer further injury, do not move the victim.
First aid requires rapid assessment of victims to determine whether life-threatening conditions exist. One method for evaluating a victim’s condition is known by the acronym (首字母缩写语) ABC, which stands for:
A - Airway: is it open and clear
B - Breathing: is the person breathing Look, listen, and feel for breathing.
C - Circulation: is there a pulse Is the person bleeding externally Check skin color and temperature for additional indications of circulation problems.

A．some basic facts about first aid.
B．the importance of protecting the accident scene.
C．what professional medical help is.
D．who can administer first aid.