这要看具体情况了，某个先行词用什么关系词引导定语从句是不一定的，这取决于引导词在定语从句中作什么成分，作主语、宾语的，要用that或which，作状语的就得考虑用where或when。即使是day，year这样的先行词，关系词也不一定要用when，也可能用that或which。如：
I will never forget the day when I joined the Party. 作时间状语
He happened to come (on) the day that was my birthday. 作主语
The director came in person to mark the occasion that mattered to him. 作主语
He always talks like that on the occasion where（相当于on which） he can draw others' attention. 作状语。
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