资料题：Why is it necessary to transplant artificial skin instead of their own skin for some bum victims（　）。

Every year about 10,000 people in the United States die from severe buns.Severe bums allow the loss of water from the body.Once the protective covering of the skin is gone, the body is also in great danger of bacterial infection.When someone has been burned.the most importantfirst step is to close the wound.The best way to close the wound is to transplant (移植) skin from another part of the victim's body.Unfortunately, some bums affect such a large area thattransplanting the patient's own akin is not possible.Fortunately chemical engineers have recently developed a new product to help bum victims.This product is artificial (人造的) akin.Artificial skin can quickly cover and protect large areas of burned skin.Artificial skin is a two-layer material made of tissue from cattle.It is only two-hundredths of an inch thick.This material guards against infection and the Loss of fluids while the patient's skin grown back.Over small wounds, artificial akin is eventually shed (脱落) as natural skin underneath heals.Over lager wounds, the artificial skin lasts up to 40 days before it breaks down and a new are must be used.Artificial skin may help save the lives of thousands of bum victims.