题目

Different types of maps have different uses. Tourist maps, for example, have signs to show places of interest in an area. When tourists read these maps, it is easy for them to find where to go and what to see in a place and it is easy for them to go and find their ways to these places. Road maps show large areas so that people can plan long journeys. Different types of roads are given different numbers. For example, if you want to go to Wood Green, you just follow No. 621 Road and keep looking at the road signs.Distribution maps (分布图) use colors or signs to show facts about an area. Fo函数y=的图象是双曲线，且在每个象限内函数值y随x的增大而减小，则m的值是（ ）A．-2B．4C．4或-2D．-1