Someone knocked at the door when(while) I was having breakfast. ^{正在doing 的时候另一件事发生了。}

When(while) I was leaving the house, the postman arrived. ^{从句在前(一个动作在进行时，另一也发生了)}

Just as(while) I was opening the front door, the telephone rang. ^{恰好在我打开前门的时候，电话响了。}

She slipped and hurt herself while(when) she was getting off the bus. ^{while接进行时态，但这里也可以替换成when.}

He cut himself while(when) he was shaving. ^{过去式+过去进行时}

My wife was cooking the dinner while(as) I was working in the garden. ^{双进行时态(对应不同主语My wife and I )}