过去进行时和一般过去时有什么区别?

过去进行时和一般过去时有什么区别?
When I was doing the housework,my husband telephoned me from the office.While I was listening to the stereo,my mother came into the room.While I was cooking the dinner ,he was working in the garden.为什么句中又有过去进行时,又有一般过去时,究竟是什么时候,用一般过去时 什么时候用过去进行时.when和while的用法是什么啊