来源：学生作业帮 编辑：作业帮 时间：2019/07/19 14:12:00
I was cooking at the kitchen when I heard somebody knock the door.
I heard someone knocked at the door when cooking.
I heared someone knocked the door when I was cooking.
I heard someone knocking at the door when I was cooking.
hear sb. doing sth.
I heard someone knocking at the door while cooking.
I was cooking while someone knocking at door.
1. I heard someone knocking at the door when I was cooking in the kitchen
2. when I was in the kitchen, I heard someone knocking on the door.
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