题目

More highways have been built in China, ___________it much easier for people to travel form one place to another.                                                                A. making      B. made        C. to make    D. having made   答案：A 用皮带运输机把货物送往高处，在运送货物的过程中，货物所受摩擦力的方向为________；货物受到的是________(选填“静摩擦力”或“动摩擦力”)，这个力是________(选填“动力”或“阻力”)．