happen作“发生、碰巧”解,常用于偶然或突发性事件,例如:
Whathappenedtoyou?(一般不说:Whatdidyouhappen?)
Maybesomethingunexpectedhappened.
Ihappenedtoseehimonmywayhome.
=IthappenedthatIsawhimonmywayhome.
comeabout表示“发生、产生”,多指事情已经发生了,但还不知道为什么,常用于疑问句和否定句,例如:
WhenMotherwokeup,shedidn’tknowwhathadcomeabout.
I’llneverunderstandhowitcameaboutthatyouwerelatethreetimesaweek.
Doyouknowhowtheairaccidentcameabout?