单项选择题
The number of phone calls arriving at a switchboard each hour has been recorded and the following frequency distribution has been developed. What is the cumulative frequency of the third class？（）
A.80 B.0.40 C.155 D.75
单项选择题 A cumulative frequency distribution would provide（）.
单项选择题 Which of the following is best to show the percentage of a total budget that is spent on each category of items？（）
单项选择题 One rule that must always be followed in constructing frequency distributions is that （）.
