题目

China Daily Oct. 11, 2008 —The Ministry of Health has called for more awareness from the public on the mental health of the young, as part of efforts to mark the World Mental Health Day which fell on Friday.  More than 15 percent of Chinese youths have been found with mental problems, and about 30 million young people under 17 are suffering from depression, the Shanghai-based Wenhui Daily reported. The World Health Organization estimates that before 2020, the rate of children with mental problems will increase to 50 percent, and mental problem will become a major factor behind deaths and il 人体中缺乏某种元素会影响身体健康，甚至引起疾病．例如导致骨质疏松、畸形所缺的元素是 [　　] A．锌 B．钙 C．碘 D．铁