still: applies to what is motionless and adds the implication of hush or absence of sound: the ~, dark night.


quiet: like still, may imply absence of perceptible motion or sound or of both but it is likely to stress absence of excitement or turbulence and connote tranquility, serenity, or repose: a ~ town.


silent: may apply to motion or stir unaccompanied by sound and carries a strong impression of silence: a submarine equipped for ~ running.


noiseless: also applicable to soundless motion, usually connotes absence of commotion or of sounds of activity or movement: a cat slowly advancing on ~ feet.


still: 既无声音也无动作，quiet: 同still，但强调平静休憩无搅扰，silent: 指动作时无声静音(如老电影)，noiseless: 同silent


记忆方法: 1) 首字母SQSN联想为申请声纳<==检测安静物体

               2) 安静的意思是不搅扰吵嚷mean making no stir or noise.首字母SQSN联想为申请声纳<==检测安静物体