题目

—Shall we ask Bob to help us do the work? —Sure. Time _____and we have a lot to do tonight. A . is run out B . is running out C . has been run out D . was run out 答案：B山区的公路多修成环绕山坡的盘山公路，这样车辆向上行驶时可以（ ）A.提高功率B.提高机械效率C.减小所必需的牵引力D.减小所做的功