青藏高原地区商业网点稀疏的主要原因是
①土地面积小 ②水源不足 ③人口稀疏 ④交通不便
A．①②
B．②③
C．③④
D．②④
答案：C
参与生物氧化的维生素是（）
A.生物素
B.核黄素
C.硫胺素
D.钴胺素
E.泛酸
The most effective first aid treatment for chemical burns is to immediately（）.
A.apply ointment to the burned area
B.flood the affected area with water
C.wrap the burn with sterile dressing
D.apply an ice pack to the burned area
