Question

This is research center______ you visited the modern equipment last year?

This is the research center _____you visited the modern equipment last year?
关系代词怎么填？

Answer 1

where 后面的主谓宾完整。
很高兴为你解答！
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Answer 2

where

Answer 3

where
you visited the modern equipment last year in the research center.
所以先行词在句中作地点状语。