单项选择题

某运输企业每年耗用材料甲15000千克，每一次订货成本为1200元，每千克材料甲储存成本为6元，材料甲单价为20元/千克。
每次的经济订货批量为（　　）千克

A.720
B.2449.49
C.1982.37
D.1500

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Scientists have devised a way to determine roughly where a person has lived using a strand(缕)of hair, a technique that could help track the movements of criminal suspects or unidentified murder victims.The method relies on measuring how chemical variations in drinking water show up in people's hair.'You're what you eat and drink, and that's recorded in your hair,' said Thure Cerling, a geologist at the University of Utah.While U. S. diet is relatively identical, water supplies vary. The differences result from weather patterns. The chemical composition of rainfall changes slightly as rain clouds movE.Most hydrogen and oxygen atoms in water are stable, but traces of both elements are also present as heavier isotopes(同位素). The heaviest rain falls first. As a result, storms that form. over the Pacific deliver heavier water to California than to Utah.Similar patterns exist throughout the U. S.. By measuring the proportion of heavier hydrogen and oxygen isotopes along a strand of hair, scientists can construct a geographic timelinE.Each inch of hair corresponds to about two months.Cerling's team collected tap water samples from 600 cities and constructed a map of the regional differences. They checked the accuracy of the map by testing 200 hair samples collected from 65 barber shops:They were able to accurately place the hair samples in broad regions roughly corresponding to the movement of rain systems.'It's not good for pinpointing (精确定位),' Cerling saiD.'It's good for eliminating many possibilities.'Todd Park, a local detective, said the method has helped him learn more about an unidentified woman whose skeleton was found near Great Salt LakE.The woman was 5 feet tall. Police recovered 26 bones, a T-shirt and several strands of hair.When Park heard about the research, he gave the hair samples to the researchers. Chemical testing showed that over the two years before her death, she moved about every two months.She stayed in the Northwest, although the test could not be more specific than somewhere between eastern Oregon and western Wyoming.'It's still a substantial areA.' Park saiD.'But it narrows it way down for mE.'What is the scientists' new discovery?A.One's hair growth has to do with the amount of water they drink.B.A person's hair may reveal where they have liveD.C.Hair analysis accurately identifies criminal suspects.D.The chemical composition of hair varies from person to person.

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下列关于航空公司产品成本的分析，正确的有（）。

A.航空公司产品成本包括旅客层次、航班层次、航线层次和航线网络层次四部分
B.客桥服务费发生在离港服务和进港服务进程
C.客舱服务费和旅客服务费属于航班层次成本
D.航线网络层次成本是航空公司进行航班运行和旅客服务的物质基础
E.航班层次成本即每个航班的边际成本

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