present perfect tense

Hi

Present perfect tense
現在完成式係表示從過去某個時間點開始的動作
到目前已經完成
或一直持續至今

例: I have lived in Singapore for twenty years.


Past perfect tense
過去完成式的動作係始於過去的過去

例: We had known each other for ten years before we got married.

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Present perfect tense is used to describe something happened in the past and it connects to present and probably continues in the future Or something has just happened.
Past perfect tense can be used in 1. reported speech when you report the original statement in simple past tense or present perfect tense; 2. like the examples below that the event had happened in the past and completed before another event happened.
If change your examples into the following, it may help to illustrate the usage.
a. Her plane had just landed before we got to the airport.
b. After she had just left the room, the police arrived.

2010-06-13 16:44:18 補充：
Example of present perfect tense:
I have lived in Tsuen Wan for five years.
So far, he has collected a variety of antiques.

2010-06-16 18:10:03 補充：
In reported speech, present perfect tense is changed to past perfect tense.
I said the other day that I had lived in Tsuen Wan for five years.
He said that he had collected a variety of antiques.