since : 這兩句有什麼分別 ?

這兩句在文法上都是對的，只不過since在這兩句發揮的功用不同。在第一句裏，since作為副詞，是用來修飾seen[怎樣未曾看見(haven't seen)─自從那時到現在(since)]
如:
ad.(常用於現在完成式或過去完成式)
1. 此後;從那時到現在
She left school three years ago and has worked as a nurse ever since.
她三年前畢業,從那時起便一直當護士。
而第二句的since是作為一個連接詞用，如：
conj.
1. (常用於現在完成式或過去完成式)自...以來,從...至今
It's been ten years since they married.
他們結婚到現在已經十年了。
She has been living a hard life since her husband died.
自從丈夫死後,她一直過著艱苦的生活。

所以，兩句都對，只不過since在兩句中功用不同。

2007-04-22 08:06:49 補充：
你這兩句在意思上分別並不大，第一句是1) He left the next day and we haven't seen him since.（他隔天便離開了，此後我們再沒有見過他）2) We haven't seen him since he left the next day.（自從他隔天離開後，我們便再沒有見過他）這兩句不但在意思上相近，這兩種寫法也有很多人用。

一)
1)錯
2)對

三)
第一句應該寫作:"He left the next day and we haven't seen him since then."

1) He left the next day and we haven't seen him since.

2) We haven't seen him since he left the next day.

請問 :

一) 以上兩句哪一句是錯的, 還是兩句也是對的 ?
1)錯
2)對

二) 假如兩句是對的, 可否說出意思上有什麼分別, 和哪一句較通用呢 ?
既然1係錯,咁就唔用
意思上一樣,係文法錯


三) 假如有一句是錯的, 可否說出錯在哪裡 ?
1) He left the next day and we haven't seen him since
since應放中間,and先講所以...再講點解
so係We haven't seen him since he left the next day