题目

You had better get all the people __________ the work, or you can’t get it ________on time. A. do, done                B. doing, do                C. to do, done              D. done, done 答案：C仔细观察下列三个实验，并回答：图1实验说明发声的物体在______；图2实验表明静止的砝码具有______；图3实验说明力可以改变物体的______．