Is the factory --------we visited last year

答案：C
这是一个疑问句语序,我们把他变成陈述句语序就能很好理解了,即：The factory is the one (that) we visited last year.这句中,the one是特指,指代前面的the factory,关系代词that在定语从句中作visited的宾语,可以省略.如果答案选A的话,这个句子就不完整,因为定语从句通常是修饰名词或代词的,可以省略,即：Is the factory?很显然,这是错误的,所以答案是C,而不是A.