問問有關英文句子既問題

由於你沒有提供前文後理和句子的背景，所以以下只可以從文法的角度分析句子。

你使用了現在完成式 (present perfect tense)。
句子的文法是無錯的。

I have finished throwing away the letters.
我已經完成了丟棄信件。

have finished 這個部份是主動詞的部份。
由於用了 finish，後接的動詞 throwing 要用動名詞 (gerund) 的形式出現。


圖片參考：https://s.yimg.com/rk/HA00430218/o/1457336257.jpg

知足常樂所言甚是，真的要看你的前文後理。文法是無錯，'the letters'係ok嘅，如果你的前文有提及過那些信。
eg： A man is walking down a road. There is a dog with the man.

The present perfect" have finished" denotes present result of past actions.
Note that the words "away"=out
the word"the letter"=all the letters;
the word"for"=for all the letters referred, when we refer to a period of time.
throwing=a gerund in the form of the present participle of a verb=throw,ending in --ing, for two verbs can't be written in a sentence(grammar).
Hence:-I have finished throwing away (all) the letters lee.