Is this research center ________ you saw the modern equipment last year?
A.whichB.thatC.the one thatD.the one where在线课程D
将疑问句改为陈述句：this research center is…显然缺少先行词，必须加上代词the one来作先行词，又因定语从句不缺主语或宾语，所以用关系副词where。假若在this后加the，就选where，请想想这是为什么。