I was about to leave when the telephone rang.为什么ring不用现在进行式

I was about to leave home这里的about to是什么用法? The carpenter was about to leave. ()Yesterday morning I was just about to leave ___ to telephone rang.A when B while I was about to leave when it began to rain可否与suddenly 连用 I was about to I _______________ the office when the telephone rang.A.was about to leave B.would leave C.left D.was to leave选哪个为什么? I was about to leave when I suddenly hear someone above_____A to speakB speakingC being spokenD was spoken I was about to leave when the telephone rang.为什么ring不用现在进行式 I was about to leave.这句话的意思是：我正要出门.请问：about在这句中的作用? 问下这两个英语句子之间的差别1.I was about to leave when suddenly the telephone rang.2.I was about to leave when suudenly the telephone was ringing i ——to visit him yesterday,but someone came to see me just when i was about to leave——处 选填plan一种时态 I was about to leave my house when the telephone rang.我正要离开我的房子的时候,电话铃响了.about I was about to leave the airport -----someone called me.A before B whenC afterD the momentBD有区别吗?be about ……when固定搭配？ I was (to have left) for Macao last Friday,but i changed my mind.A to leave B to have left C about to leave D to be leaving我知道I was to have done表示本来应该已经干了某事（暗含意思是现在没有做）是正确答案,而about to I was about to finish my work. as i was about to go I was here,you gave me to leave immediately i was supposed to leave 这里的to leave 什么成分