某厂某年职工劳动生产率为20000元，是历史最高水平的1.2倍。这里的1.2倍是（）

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 approximate range of the number of phone calls arriving each hour？（）

A.80
B.200
C.20
D.100

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（）.

A.a graph of a frequency distribution
B.a running total of the frequencies in the classes
C.the proportion of the total frequencies which fall into each class
D.a very cloudy picture of the frequencies

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？（）

A.histogram
B.ogive
C.stem and leaf chart
D.pie chart

单项选择题One rule that must always be followed in constructing frequency distributions is that （）.

A.the number of classes must be less than 10
B.each data point can only fall into one class
C.the width of each class is equal to the range
D.the number of intervals must be an odd number