【单选题】He kept on ____ and swimming.
【单选题】He kept on ____ and running.
【简答题】什么是碳素钢? 2、钢中常存元素对钢性能的影响是什么?
【简答题】He kept on writing and writing,he has finally become a famous writer.
【简答题】He kept on running and running.
【判断题】机械循环上供下回式系统水平敷设的供水干管应沿水流方向设上升坡度,坡度值不小于0.002,一般为0.003。( )