past tense / past perfect tense

1) I wrote a letter yesterday. (Simple Past tense) [RIGHT]
2) I had written a letter yesterday. (Past Perfect tense) [WRONG]
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你的例句用Simple Past tense去表達就正確啦, 不宜用Past Perfect tense. 為何呢?
Simple Past tense係用作形容一件已過去的事情 (那件事在過去時開始, 亦已在過去時完成) 而有明確的發生的時間, 例如yesterday, one year ago, last week, when I was a child, when I lived in Japan, at that moment, that day, one day, etc.
其實, Simple Past tense和Present Perfect tense更容易混淆不清.
1a) I have seen three movies this week. (這星期還未過去, 所以用Present Perfect, 而不是Past tense)
1b) I saw three movies last week. (上星期已經過去, 所以用Past tense)

2a) Martin has crashed his car again. (這是最近/ 最新的資料, 所以不用Past tense)
2b) Martin crashed his car last year. (重提舊事, 這是上年的舊料, 所以用Past tense)
3a) I have seen that movie. (我唔記得幾時睇, 只記得係曾經睇過)
I saw that movie on Thursday. (明確記得幾時睇, 所以用Past tense)

3b) I have lived in Victoria for 5 years. (我現在仍然住在Victoria, 所以用Present Perfect tense, 而不用Past tense)
I lived in Victoria for 5 years. (我現在已經不再住在Victoria, 這完全是過去的事, 所以用Past tense)
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Past Perfect tense一般係用作比較兩件已過去的事, 說明其中一件事發生在另一件事之前.
I did not have any money because I had lost my wallet. 「沒有錢用」和「遺失錢包」這兩件事都已經過去, 但「遺失錢包」的事係發生在先, 以致「沒有錢用」.
Had Susan ever studied Thai before she moved to Thailand? 在移民到泰國之前, Susan有否曾經學過泰文呢?
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所以, 根據以上例子, 你的例句應用Simple Past tense因為
1) 有確實發生時間.
2) 只有「寫信」一件事, 而並非比較過去兩件事.

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

好勁呀你,你明白個tense的用法呀~!!

兩句都對,意思有d唔同

我想話我昨天寫了封信：
1) I wrote a letter yesterday 就用這一句

我好肯定昨天己經寫左信
2) I had written a letter yesterday 就用這句

1) I wrote a letter yesterday. (correct)
2) I had written a letter yesterday. (wrong)
Because you want to describe something in the past and the action was complete.

But your example is present perfect tense woo~~^^

1 is better!
It's because you are saying what you did yesterday, so you use past tence.
The second one(2) is usually use for something you started to do it some time ago, but now you are still doing it, then we will use the second one. E.g I has lived in Hong Kong 12 years ago. which means I live in Hong Kong am living in hong kong for 12 years, and now i am living in Hong Kong also.