這要看具體情況了，某個先行詞用什麼關係詞引導定語從句是不一定的，這取決於引導詞在定語從句中作什麼成分，作主語、賓語的，要用that或which，作狀語的就得考慮用where或when。即使是day，year這樣的先行詞，關係詞也不一定要用when，也可能用that或which。如：
I will never forget the day when I joined the Party. 作時間狀語
He happened to come (on) the day that was my birthday. 作主語
The director came in person to mark the occasion that mattered to him. 作主語
He always talks like that on the occasion where（相當於on which） he can draw others' attention. 作狀語
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