fall 、drop的区别：
fall指东西由高处向下坠落,不及物动词；也可以作连系动词,意思是“变得,进入某种状态”。drop表示物体由高处往低处落下,不及物动词；或让物体落向低处,及物动词。如：The man fell off the tractor and hurt himself. (那个人从拖拉机上摔下来跌伤了)/ Soon after they touched the pillows they fell (系动词) fast asleep. (他们头挨枕头不久就睡着了)/ He felt as if he had to drop maths.(他觉得似乎要放弃数学)/ He dropped a letter into the mail-box.(他向邮箱里丢了一封信)