he was still smiling when the door opened and his wife came in

问题描述:

he was still smiling when the door opened and his wife came in
the door opened,我听过open the door,这里是怎么回事?

这是一个句型
be (过去进行时) doing something when something else happened (过去时)
他仍在笑时门开了,太太走了进来.(说明他没想到太太会在这里到来.)