克山病是由于缺乏微量元素
A．铜
B．硒
C．锌
D．铁
E．碘
参考答案：B
解析：克山病、心肌缺血、癌、多发性硬化症、肌营养不良等时血硒降低。
I'm not surprised that he became a writer. Even as a child he had a ________ imagination.[ ]
A. clear
B. cautious
C. funny
D. vivid
网络教育的主体是学校，网络学习的主体是学生。
s a child he had a ________ imagination.[ ]