填that因为这是一句定语从句,the factory 是先行词,在定语从句中做visited的宾语,所以需要填关系代词that ,而the one不能做关系代词引导定语从句。
B.the one指代factory在主句中要充当成分,而前文已经出现the factory 而且还原句子this Is the factory中不缺成分,用.that 引导的是同位语从句
This is the factory that you visited the other day !不缺少先行词!先行词是factory!所以你要加the one 就 多余了!若改为;Is this factory -----you visited the other day 就可以了 选B!所以本题答案是A!
因为that 可以做定语从句的先行词,而the one 不可以。