1).take place 表示“发生、举行、举办”,一般指非偶然性事件的“发生”,即这种事件的发生一定有某种原因或事先的安排,例如：
Great changes have taken place in our hometown during the past ten years.
(2) .happen作“发生、碰巧”解,一般用于偶然或突发性事件,例如：
What happened to you?(一般不说：What did you happen?)
Maybe something unexpected happened.
I happened to see him on my way home.