help最不正式,特指靠本身力量无法解决的,迫切需要的帮助;
Building more motorways and bypasses will help the environment by reducing pollution and traffic jams in towns and cities...建造更多的高速公路和绕城道路能够减少城镇中的污染和交通堵塞，有利于改善环境。
aid正式些;
They have already pledged billions of dollars in aid.他们已经许诺援助几十亿美元。
assistance最正式,来自assist,只表示起到辅助作用.
Any assistance you could give the police will be greatly appreciated...您提供的任何帮助警方都将万分感谢
aid 英 [eɪd] 美 [ed]
shchengzhang
