just as we were teaving,the postmon(knoked\was knocking)at the door

Question

选择括号内的

Answer 1

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。

Answer 2

knocked