關代前面的介係詞用法

Question

如題,例如:
Reviewers praised her for her use of the epistolary form,( in) which written correspondence between characters comprises the content of the book, and her ability to use black folk English.
括號的地方就是我的疑問,為啥還要再加個介係詞呢??

Answer 1

１.『介詞＋關代』的用法，有以下幾個重點：
　　介詞是由後面動詞片語中的介詞往前移
　　『介詞＋關代』時，關代雖然是受格，但不可省略
　舉個例子：
　He is the boy whom I am looking for.
＝He is the boy for whom I am looking.
２.關係副詞：
　等於『介詞＋關代』
　關係副詞前的先行詞『可省略』
●　關代＋『不完整子句』。不完整子句就是子句內缺主詞或受詞。
　　　關副＋『完整子句』。
Ｅｘ.This is the village which I visited last year. ←缺受詞
　　 This is the village where I was born.
where I was born → I was born （in the village）
　↑ˍˍˍˍˍˍˍˍˍˍˍˍˍˍ↑
－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－以上僅供參考。
至於為何加介係詞，在 which連接的子句中，written correspondence between characters 是主詞，comprises 是動詞，the content of the book, and her ability to use black folk English 是接受 comprises 的受詞。
　　　　　　　　　　Ｓ　　　　　　　　　　　　　Ｖ　　　　　Ｏ
which（ written correspondence between characters）（ comprises）（ the content of the book, and her ability to use black folk English）『in』 the epistolary form.
此處的 in指的是在 the epistolary form 裡。

Answer 2

The way of "candidate 2" I totally agree.

Well,we could take "in" out.

It's o-k-a-y toooooooooo.

Answer 3

因為 which 是指 epistolary form 這個名詞，而名詞後面不能直接加 written correspondence between characters comprises the content of the book 這個完整的句子 (主詞是 written correspondence between characters，動詞是 comprises，受詞是 the content of the book)，一定要有介系詞才行。

希望可以幫忙~~