1.选a.that引导定语从句,修饰the factory,并且that在从句中做的visit的宾语.(记住:定语从句的引导词,如that,在从句中一定要做某个成分)B不能选,是where引导的是地点状语从句;C不能选,因为visit是及物动词,后边不需要加介词,否则就成了 visit in a place了.
2.d.完整的应该是Is the factory the one which / that some foreign friends visited last friday?原句中省略了that / which.前面的 Is the factory,是强调和特指,所以要用the one.
3.b.这儿的where就引导的地点状语从句.从句he works ten years ago并不缺少任何成分,所以不可能是定语从句.