题目

Several different stories are told about the origin of Saint Valentine’s Day. One legend(story) dates as far back as the days of Roman Empire. According to the story. Claudius, the Emperor of Rome, wanted to increase the size of the army. He knew that it would be easier to get young men who were not married to join the army; therefore, he made a rule that no young men could marry until he had served in the army for a number of years. A priest(man working in church) named Valentine broke the rule and secretly married a great number of young people. Finally, Claudius found out about Valentine 如图为一列简谐横波某时刻的波形图，已知质点P此时的运动方向如图所示，则（ ）A．波向右传播 B．此时质点a的加速度为零C．质点a比b先回到平衡位置 D．质点c与p的运动方向相同