题目

A tourist will easily lose his way in Beijing ______ he has a map or a guide.A．ifB．becauseC．unlessD．when 答案：C解析:略一定质量的理想气体，状态变化过程如p－t图中直线ab所示（直线ab通过坐标原点），根据图像可以判定           （      ）A．Va=VbB．Va>VbC．Va<VbD．无法判断