present perfect tense

I have eaten an apple.（我已經吃了一個蘋果）
對，這是一般的 present perfect tense，可強調「一件事已經發生」（比 past tense 更強調「已經」這個意思）當然，在加強語氣的話，你可加 already： I have already eaten an apple.


I haven't eaten an apple.（我還沒有吃過一個蘋果）
不對，eat 的 past participle 是 eaten，並沒有 eatten 這個字。
另外，最後可加個 yet 來加強語氣，I haven't eaten an apple yet.


An apple has been eaten by me.
不對，第一，一個蘋果智能夠「被吃掉」，故此 apple 作為一句句子的 subject（主語），應用 passive voice（被動式），而非像這裡用 active voice（主動式），所以要 been

第二，正因為 an apple 這個 subject 是單數的，後面的動詞也要跟著用單數，即 has 而非 have。

要檢查清楚哪個是 subject 哦，動詞是單數或複數是要看 subject 的。



希望幫到你。


2013-08-09 16:28:18 補充：
不對，上面解釋過，所以不再重覆了。

三句的正確答案:
I have eaten an apple.
I haven't eaten an apple.
An apple has been eaten by me

Present perfect Tense 從 active voice 轉去 passive voice

Present perfect Tense 格式 (Active voice 主動語態)
Subject + have/has + verb (past particle) + object [active voice]

(I, You, We, They, The monkeys) + have + eaten + an apple.
(He, She, John, The monkey) + has + eaten + an apple.

轉去 passive voice 程序
原本 subject 變成 object. 原本 object 變成 subject .
即是 subject 和 object 互相對換
當 pronoun (代名詞) 從 subject轉去 object時, 除了you和 It, 其他要轉 form
I – me, We – us, They – them, He – him, She – her
其他不變You – you, It – it, John – John, monkey – monkey, monkeys - moneys

Passive voice 句子, 加添個 been, 在 have/has 後面, 在 object前面有個 by
Third person singular (第三者單數) 用 has, 其他用 have,

Present perfect Tense 格式 (Passive voice被動語態)
Subject + have/has + been + verb (past particle) + by + object [passive voice]

An apple + has + been + eaten + by + me, you, us, them, him, her, John, the monkey(s)

Two apples + have + been + eaten + by + me, you, us …..John, the monkey(s)

結論:
I have eaten an apple.~ 對
I haven't eaten an apple. ~ 對
An apple have eaten by me. ~ 錯
An apple has been eaten by me. ~ 正確 answer

An apple 第三者單數要用 has, 同時遺漏了個 been 字

Compare:
Two apples have been eaten by me. (~ subject 是第三者複數)