弹簧振子以O点为平衡位置,在B、C两点间做简谐运动,在t=0时刻,振子从O、B间的P点以速度V向B点运动;在t=0.20s时,振子速度第一次变为﹣V;在t=0.50s时,振子速度第二次变为﹣V.
①鹦鹉学舌 ②蜘蛛结网 ③孔雀开屏 ④老马识途
—Excuse me, where is the bookstore? —Go _____ the bridge. You'll see it on your left.