why the auther use ”of which” instead of ”which” ?

睇過兩位前輩的答案,我較偏向 STEVIE-G™ 的答案, 因為我認為用of 定唔用of, 並唔影響which 代表邊個字, 而唯一會影響的是, 如果唔用of字, 句子根本唔能夠表達到應有的意思。

STEVIE-G™ 前輩的答案, 已經引用到一個相似的例句, 但係解釋可以再深入D。究竟咩情況, 在relative clause 內的 relative pronoun前面要多個 preposition呢? 原因係, 當主句的subject 唔等於又或者唔係完全等於relative clause的 subject, 讓我引用STEVIE-G™ 前輩的例句再作解釋。

1) HK is a beautiful place. (HK係此句子中的subject)

2) Tom lives in HK. (但在這裏, HK只係此句子中係object, 而Tom先係subject)

當第二句轉做relative clause, 插入第一句時,HK就要變成which, 而跟in同時調到relative clause的最前位置。

HK, in which Tom lives, is a beautiful place.

另一個情況就係好似你問題中的那句句子。等我先將句adverbial phrase抽開, 令句子易睇D。

According to the latest budget figures, stamp duty raised more than 14 billion pounds in the last fiscal year, of which around 70 percent came from property.
根據最新的預算案數字, 在過去一個財政年度, 印花稅上升的幅度逾140億英磅, 當中的 7成收益是來自地產方面。

如果將relative clause折出就易睇得多啦!
70 percent of the stamp duty (= which) came from property.
這句子中的subject 係 "70 percent of the stamp duty" (noun phrase).

但 相比佢的主句(subject 係 The stamp duty), 主句的subject "The stamp duty" 只係relative clause 的 subject "70 percent of the stamp duty"的一部份, 為保留佢只係「一部份」的意思, of 必定係唔可以刪除。正如以下句子, 無咗of 字, 你又覺得通唔通呢?

70 percent (?) the stamp duty came from property.

换句話講, 當一句relative clause 插入一句主句時, 只係relative clause 內的部份文字調位(如果有需要的話), 而文字本身係仍然保留。


圖片參考：http://tw.yimg.com/i/tw/ugc/rte/smiley_1.gif

Let me use an example to illustrate...
1,HK is a beautiful place.
2.Tom lives in HK.
To link up the two sectences , we use relative clause.
HK ,in which Tom lives ,is a beautiful place.
we should put the preposition in front of the wh-word.

"of" which - the "of" is referring to the stamp duty.
If we omit the "of", then the "which" will then refer to "the latest budget figures", which has totally changed the meaning and reasoning of the sentence.