词汇训练：.用适当的词填空（共10小题，每题1分，满分10分）
As everyone knows, the skin is  （必不可少的）to us. Our skins can sometimes  (burn) due to our   (粗心). Therefore, first aid shows its importance in the（治疗） of burns. Generally speaking, burns,   are caused by hot liquids, fire, radiation and so on, can be divided into three types－first degree, second degree and third degree    (depend) on the   (受伤的) layers of the skin. To minor burns, cool water proves to be helpful in  （stop）the burning process and preventing or reducing pains. But  severe burns, get the to the doctor immediately.