一、语法填空(根据课文内容、依据语法规则完成下面短文）
The skin, which acts as 1________ barrier against disease, poisons and the sun’s 2________ (harm) rays, is an essential part of your body. So if your skin gets burned it can be very serious. Depending on 3________ layers of the skin are burned, they are called first, second or third degree burns. First degree burns make an effect only
