Is this factory___ you want to visit tommorrow.还原成陈述句后为:this factory is___ you want to visit tommorrow.可以看出主句缺少先行词,所以用the one代指先行词,其后省略了that或which.
如果改成the factory.原句还原后.
this is the factory ___ you want to visit tommorrow.先行词为the factory,在从句中做宾语,引导词that或which或省略不用.