just as we were teaving,the postmon(knoked\was knocking)at the door选择括号内的

just as we were teaving,the postmon(knoked\was knocking)at the door
选择括号内的

Just as we were leaving,the postman knocked at the door.[正当我们要离开时,邮递员敲门了.]
knock是短暂性动词,用一般过去时,而不用过去进行时.

knocked