when的用法四種句型：be doing sth…when；be about to do sth…when；hardly…when；had just done…when 。
1、be doing sth…when
例：He was still smiling when the door opened and his wife came in.
他正笑著的時候門突然開了，他妻子走了進來 。
【when的用法前后的時態 when的用法四種句型】2、be about to do sth…when…
例：We were about to start when it began to rain.
我們剛要出發，天就開始下雨了 。
3、had not done sth…when…/hardly…when…
例：He had not fallen asleep when the telephone rang.
他剛要入睡電話就響了 。
4、had just done…when…
例：I had just gone to bed after a very hard day when the phone rang.
在勞累了一天之后我剛剛就寢，電話鈴就響了 。
