關於英文hear的用法問題。?

Before是有3種詞性:

1. 介係詞:
example:
He had won many contests before college.

2. 連接詞:
example:
He had won many contests before he went to college.

3. 副詞:
example:
He has won many contests before (now).

(1)與(2)都要用 <過去完成式>是因為 時間參考點都是在過去.
(3)適用<現完式>是因為 時間參考點是現在(或是不明).

Both present perfect and past perfect tense can be used with the adverb "before" to connect earlier events to the moment of speaking or to a point of time in the past.

1. Don't try to tell me again. I have heard it all before. (up to the moment of speaking)

2. Mary told me her secret last night but I had heard it all before. (up to that point in the past)