It’s the old house.Ilived in the old house three years ago.

It’s the old house.Ilived in the old house three years ago.(合为一句）It's the old house -------I lived three years ago.中的关系词是that还是where。为什么？请高手指教
有的语法书上是这样讲的，当先行词在主句中作表语或其所对应的关系词在从句中作表语时，关系词必须用that，上面的句子属于那种情况吗？为什么？急求原因，重原因，求高手赐教。谢了。

Henry's mother was to look after the watch for Henry until he was old enough to own it It's never too old to learn.怎么解释？ It ____Mike and Lily ____helped the old women yesterday Ted opened the drawer and ___some old photos in it. The old man's left eye is blind. 3.In the old days it was difficult for the poor ____ a job. The old lady kept the little dog ______(活着) by feeding it warm milk. It was polite ______ the child _________ up his seat to the old man. it was very polite ____him to give his seat on the bus to the old man. It is not uncommon for there___problems of communication between the old and the young.