题目

产生四季的根本原因是       A．地球始终不停地自西向东自转           B．地球的公转轨道是椭圆形的       C．地轴始终倾斜于轨道平面公转               D．太阳的东升西落 答案：CThe glass door have taken the place of the wooden ones at the entrance, _____ in the natural light during the day. A．to let             B．letting            C．let               D．having let