数据字典有哪6类项目？
参考答案：
数据元素、数据结构、数据流、数据储存、数据处理、外部实体。
下列说法正确的是
A．摩尔质量就等于物质的式量
B．摩尔质量就是物质式量的6.02×1023倍
C．HNO3的摩尔质量是63g
D．硫酸和磷酸(H3PO4)的摩尔质量相等
Which of the following statements regarding confidence intervals is TRUE（）
A. The higher the alpha level, the wider the confidence interval.
B. The relationship between the alpha level and the confidence interval cannot be ascertained.
C. The lower the alpha level, the wider the confidence interval.
