Suddenly there was another knock at the door.
突然，又有人敲门。
Just as breakfast was completed there was a knock at the door.
早饭刚吃完，有人敲门。
Just when she was going to bed, there was a knock at the door.
正当她要上床睡觉时，有人敲门。
Ring the doorbell or knock at the door before you enter the room.
在你进入房间之前，按一下门铃或敲门。