关键在于能否把题干正确转换为陈述句,有人把它变为：
This is research center _________ you visited the modern equipment last year.
这是错误的,因为research center前没有冠词the,定语从句修饰先行词,先行词被限定,应该有定冠词或者其他限定词.
应变为：This research center is _________ you visited the modern equipment last year.
这样主句缺少表语,就要用the one,而且先行词在从句里作地点状语,所以用where,结果就是the one where,因此答案选D.