题目

人体中缺乏某些元素会影响身体健康，甚至引起疾病。骨骼疏松、畸形的人所缺的元素是  A．锌  B．碘    C．钙   D．铁  答案：C解析:略 As is known to us all, the Sahara Desert is a natural _____ between north and central Africa. [     ]A. barrier B. routine C. garment D. basis