按要求完成句子.We parents having dinner when someone was knocking at the door.(对划线部分提问）划线部分是：having dinner - - - - when someonce was knocking at the door?

你的题目少了东西，应该还有个were，对做某事提问，应该用疑问词what，剩余部分改为一般疑问句were your parents加在what后即可，所以答案是What were your parents doing,不可缩写，缩写过去式就不存在了，你的题目是不是抄错了？

(What're your parents doing) when someonce was knocking at the door?

你的题目少了东西,应该还有个were,对做某事提问,应该用疑问词what,剩余部分改为一般疑问句were your parents加在what后即可,所以答案是What were your parents doing,不可缩写,缩写过去式就不存在了,你的题目是不是抄错了?

What were your parents doing when someone knocked at the door?
when从句用一般过去时更好。