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 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 happen to happen to happen to ,happen 怎么用? happen to和happen at的区别： happen to do or happen doing? happen with和happen to的区别 What happen to happen to sb 意思 sth.happen to sb. happen to sb 造句 happen to 的用法 happen to sb.是什么意思? happen to be doing 发生在应用A happen for B happen to Ctake place to D发生在应用A happen for B happen to Ctake place to D occurred with 后跟SB 用happen to do和happen to sb.造句 happen to 与happen to have done 的区别是什么?