happen: is the ordinary and general term applying to whatever comes about with OR without obvious causation or intention: remembering an incident that ~ed in his childhood.   （cause原因，因果中的因，是reason的基础词因此更通用，如the cause of the train wreck火车失事的原因）


chance: regularly implies absence of design or apparent lack of causation: a man he ~d to know.


occur: stresses presentation to sight or attention: such events, when they ~, fascinate the public.  又如it never occurs to me that you are so gentle真没想到你这么绅士（讽刺的话）


transpire: implies a leaking out so as to become known or apparent: the meeting ~d as planned.


happen发生: 是普通通用词，表示任何发生，无论是否有缘由目的，chance偶然发生: 表示没有计划或原因，occur发生: 强调”使人”看到或注意到(present提交呈现)，transpire发生: 有透露出或被发现的意思，暗示发生的事开始时不为人知。


记忆方法：1）首字母HCOT想成ClOTH布没了<==发生短缺

          2）发生的意思是出现mean to come about.