题目

 —Who can reach the book on the top of the shelf? —Xiaoqiang can. He is the ________ boy in our class. A. shortest  B. strongest  C. tallest   答案：C   从某一高度平抛一小球，不计空气阻力，它在空中飞行的第1 s内、第2 s内、第3 s内动能增量之比ΔEk1∶ΔEk2∶ΔEk3=________.