happen to have down的意思那用法呢

happen to have down的意思那用法呢 happen to 与happen to have done 的区别是什么? 问个关于happen的用法的问题.happen.不是happen to do sth.那么 碰巧去做,碰巧正做,和碰巧已做.是不是分别是happen to do,happen to doing,happen to have been? happen to 未发生 happen to be doing 正在发生 happen to hhappen to 未发生happen to be doing 正在发生happen to have done 已发生是这样区别的吗?老师说是.有点不确定 happen to 的用法 happen to和happen at的区别： happen with和happen to的区别 happen to have done sth 和pretend to have done sth 的中文意思 why did it have to happen?中为什么要写did?直接写why it have to happen?还是两者的性质不同?亲 连词成句：what you think,in twenty years' time write down,may happen everyone,will,to eat,have enough food,I hoope,on earth happen to dohappen to be doing happen to have done翻译下,还有没有其他的词语也能这样用,这种用法叫什么名字,再多举些例子 Thank you ,but I have to turn down your offerturn down/away/back/off的区别 happen to happen to happen to down 与have been down的区别 We can not have that sort of thing happen/happened/to happen/happening选哪个? Do you happen to have twenty dollars on you 句中的happen 怎么翻译