适用于描述某种心理属性在时间上变化趋势的统计分析图是
A．茎叶图
B．箱形图
C．散点图
D．线形图
参考答案：D
He is the only one of the students who _____ a winner of scholarship for three years. [ ]
A. is
B. are
C. have been
D. has been
水位计的配置应采用（）种以上工作原理共存的配置方式，以保证在任何运行工况下锅炉汽包（）的正确监视。
