题目

声音在空气中传播的速度是340 m/s,人对着相距425 m的高山喊一声，听到回声需经过的时间是 A.1.25 s                                B.0.625 s C.0.8 s                                 D.2.5 s 答案：D–How did he finish the work?--I hear that he did it _______.A. in the ownB. on the ownC. of his ownD. on his own