1、根據which引導的從句而定，當從句中需要以in作介詞時使用。
例句：The school which he once studied in is veryfamous.
= The school in which he once studied is very famous.
他曾經就讀的這所學校很有名。
2、固定搭配
例句：The plane may be several hours late, in which case there's no point in our waiting.
（固定搭配：in the case) ?
飛機可能會晚點幾小時，這種情況下等待是沒有意義的。
擴展資料which是定語從句的關系代詞之壹，有且僅有兩種用法。
1、which前面有逗號，逗號前面是個名詞，which就近指代那個名詞。
例句：Tankfield emailed Pea some photos, which did not cheer Pea up.
坦克福爾德給皮爾郵件了壹些照片，卻並沒有讓皮爾高興起來。
2、which前面是介詞，介詞前面是名詞，which就近指代介詞前的那個名詞，名詞和介詞之間有無逗號均可。
例句：Tankfield once lent Pea a book from which Pea glimpsed the basics of genes.
坦克福爾德曾經借給皮爾壹本他曾經在上面瞄到過基因理論的書。