有些句子中，在關係代名詞之前會有介系詞，這是因為原子句中與先行詞相同指稱的 (coreferential) 名詞為介系詞的受詞，在以關係代名詞取代後與介系詞一併移至該子句之首。

例 1：
This is the person to whom I talked.
這一位就是我跟他說話的那個人。
👉 to whom I talked 為形容詞子句，用來修飾關係代名詞 whom 的先行詞 the person，亦即 whom = the person，而 to whom I talked 指的是 I talked to the man。

例 2：
This is the house in which he was born.
這一棟就是他在裡面出生的那間房子。
👉 in which he was born 為形容詞子句，修飾 which 的先行詞 the house。亦即 which = the house，而 in which he was born 指的是 he was born in the house。

事實上，我們也可以只將關係代名詞往前移，而將介系詞留在原處，形成：

例 1.1：
This is the person whom I talked to. (= This is the person who I talked to.)
※ 句中的 whom 並未直接出現在介系詞 to 之後，因此也可以用 who 來取代 whom。

例 2.1：
This is the house which he was born in. (= This is the house he was born in.)
※ 句中的 which 為該子句中介系詞之受詞，所以可省略。

不過要注意，當關係代名詞與介系詞同時置於子句之首時，不可用 that 作為關係代名詞，而且介系詞與關係代名詞的搭配須適當，句子才有意義：

（◯）This is the person that I talked to.
（✕）This is the person to that I talked.
（◯）This is the house that he was born in.
（✕）This is the house in that he was born.
（◯）The teacher made a speech in which she thanked us for the gift.
（✕）The teacher made a speech on which she thanked us for the gift.

答案：(A)

翻譯：這波疫情凸顯了數位互動在多大程度上無法取代真實的互動。

解說：to which 引導的形容詞子句是用於修飾和補充說明先行詞 extent（表示程度），亦即 Digital interaction is no substitute for the real thing to the extent.（在某個程度上，數位互動無法取代真實事物。）