1)be doing sth when ------正在做--------突然------

He was watching TV( when the telephone rang.)

2)be about to do sth when------正要做-------突然-----

He was about to go out( when the telephone rang.)

3)be on the point of doing sth when -----正要做------突然-----

He was on the point of gong out (when the telephone rang.)

4)had hardly/scarcely done sth when-------刚------就----/一-------就-----

He had hardly/scarcely fallen asleep( when the telephone rang.)