how the ”which” would affect this sentence?

其實這兩句沒有分別，只不過第一句用了分詞子句，而第二句是用子關係子句吧了！
但用分詞子句取代關係子句，有一個原則：子句動詞是主動語態，要用現在分詞，若是被動語態，就用過去分詞
如：a letter that shows his name可以寫成 a letter showing his name
　　the name that is shown in the letter可以寫成the name shown in the letter

希望幫到你！

2008-08-22 14:52:31 補充：
hawddle，很高興可以與你一起探討

This brings us to the last of the types of adjectivals—relative
clauses, which are a new structure. In a way, though, we have
been already considering sentences that contain a sort of relative
clause. Consider these two sentences:

2008-08-22 14:52:49 補充：
Exhausted by her evening of intense play, Bonnie
fell asleep immediately.

Bonnie, who was exhausted by her evening of
intense play, fell asleep immediately.

2008-08-22 14:53:05 補充：
A participle phrase is a kind of reduced relative clause; we could
call them an “elliptical” relative clause, meaning that they are
like a relative clause, except that a few words are missing.

2008-08-22 14:53:17 補充：
The　missing word is the is relative pronoun, which begins
most relative clauses. You are already familiar with these words:
who which that whose whom

2008-08-22 15:47:00 補充：
前面的一段英文是引自”教學網站”，所以，我們可以看：participle clause為簡化的relative clause。請看以上的例子，就可知道，就自是non-defining relative clause也可以用participle clause取代。

My opinion is that the "which was" has no influence nor usage in the sentence at all.
The sentence is still clear and clean enough to convey its idea.

先o黎理解下呢句o野先。
Some real estate agents have complained that media speculation that the government could try to help the market by suspending property tax, which was known as "stamp duty," was aggravating the situation.
以上藍色部份為主句：「一些地產經紀投訴傳媒抄作使處境變差。」
紅色部份講解云云傳媒抄作之中，邊一ｄ令處境變差：「政府可能會嘗試以暫停物業稅來幫助樓市。」由於冇左呢個補充，你就唔知係乜o野抄作，唔可以界定詞語何所指，所以呢個子句叫做 defining relative clause（界定關係子句）。習慣用法，往往將 relative pronoun (that) 省略。
橙色部份o既作用呢？你已經知道乜野係物業稅，但呢句子句就再加多ｄ資料你睇：「又稱『印花稅』。」呢個資料其實可有可無，唔會影響你理解本文，所以呢種子句叫做 non-defining relative clause（非界定關係子句）。
呢種子句o既 relative pronoun 一定要保留，同句子其他部份，一定要用 comma 分隔（如上句所示）。所以，如果你刪去 which was，唔只令句意混亂，簡直係文法錯誤。

2008-08-08 17:38:01 補充：
再此都想同 hahatse 交流一下：

我初看次句時，都冇諗到係 participle clause 呢個情況，原因係 known as "stamp duty" 前後有 comma 隔開。咁o既情況下，應視之為 participle clause 定係 non-defining clause？

有個WHICH 可以清晰d話比人听property tax was known as "stamp duty,"
冇個which 就好似冇指明,講清楚咩known as stamp duty