题目

Canada has vast areas of wilderness, from the Arctic north, _______ average winter temperatures are usually -20 0C, to the border with the USA in the south, _______ is said to be the longest border in the world not defended. A. which, where  B. whose, which   C. where, where   D. where, which   答案：D水平面上甲、乙两物体，在某时刻动能相同，它们仅在摩擦力作用下停下来。图中的a、b分别表示甲、乙两物体的动能E和位移s的图象，则：    A．若甲、乙两物体与水平面动摩擦因数相同，则甲的质量较大B．若甲、乙两物体与水平面动摩擦因数相同，则乙的质量较大C．若甲、乙质量相同，则甲与地面间的动摩擦因数较大D．若甲、乙质量相同，则乙与地面间的动摩擦因数较大