prevent: implies the existence of or the placing of an insurmountable obstacle: the blizzard ~ed us from going.  （surmount克服解决;位于顶端means to deal successfully with a difficulty; or to be on the top of something，如severe technical problems to be surmounted严重的技术问题需要解决，如she was well aware of the difficulties that had to be surmounted她清楚必须克服哪些困难，如the island is surmounted by a huge black castle岛的最高处耸立着一座巨大的黑色城堡）


preclude: implies the existence of some factor that shuts out every possibility of a thing's happening or taking effect: an accident that ~ed a career in football.


obviate: suggests the use of forethought to avoid the necessity for unwelcome or disagreeable actions or measures: his resignation ~ed the task of firing him.


avert: implies the taking of immediate and effective measures to avoid, repel, or counteract  threatening evil: deftly ~ed a hostile corporate takeover.   deftly轻巧娴熟


ward off: suggests a close encounter and the use of defensive measures: a hot drink to ~ a chill.  寒冷着凉to catch a chill==to catch a cold感冒
着凉

prevent阻碍阻止: 表示设置难以克服的障碍，preclude阻碍阻绝: 表示完全阻绝，排除任何可能性，obviate避免:  表示预先考虑行动，从而避免了去做不希望做的事情的必要，avert避免阻抗: 指采取立即有效措施，将威胁伤害予以避免反击抵消，ward off抵御: 比喻短兵相接予以抵御


记忆方法: 1）首字母PPOAW排列成PAWOA怕我啊<==阻止

         2）阻止的意思是使某事停止mean to stop something from coming or occurring.