I () my brother when someone knocked at the door

问题描述:

I () my brother when someone knocked at the door
I () (telephone)my brother when someone knocked at the door

I ( was telephoning )my brother when someone knocked at the door. 一定要用过去进行时,这是一个固定句型:sb. be doing sth. when ... 某人正在做某事,这时突然... 句意:我正在给哥哥打电话,这时突然有人敲门....