运输途中发生整车运输票据丢失时，丢失单位或处理站应于（）h发电报向有关站查询。
A.48
B.36
C.24
D.12
参考答案：C
Last year, an appliance store sold an average (arithmetic mean) of 42 microwave ovens per month. In the first 10 months of this year, the store has sold an average (arithmetic mean) of only 20 microwaves per month. What was the average number of microwaves sold per month during the entire 22-month period ？（）
A.21
B.30
C.31
D.32
E.44
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