题目

弹簧振子做简谐运动，振子运动范围为0.8cm，周期为0.5s，计时开始时具有正向最大加速度，则它的振动方程是（） A . x = 8 ´10-3 sin(4pt + )( m ) B . x = 4 ´10-3 sin(4pt - )( m ) C . x = 8 ´10-3 sin(2pt + )( m ) D . x = 4 ´10-3 sin(2pt - )( m ) 答案：BMore patients _____ in hospital this year than last year. [     ]A. treated B. have treated C. had been treated D. have been treated