※ 引述《DANIELHSIANG (丹丹)》之铭言：
: 最近备课康轩版
: 里面特别提到since不能加ago
: 但之前在教复习讲义及一些文法书中
: 都有提到since 加一段时间ago
: 到底哪种才是对的？
: 有先进可以来讨论一下吗？
Can since and ago be used together?
There is no grammatical rule preventing this combination, and occasionally
expressions using both (such as 'since one minute ago' in direct answer to
the question 'since when?') may be encountered. Generally, however, we use a
for-phrase to form a period adverbial.
He has lived in Taipei for three years. (acceptable)
He has lived in Taipei since three years ago. (grammatical but unidiomatic)
Since she arrived in Tokyo two years ago, has Maryjo been really busy
managing the Dayglow Movie Studio? (acceptable) [In this sentence, "since" is
used to modify the whole clause "she arrived in Tokyo two years ago," not the
phrase "two years ago."]
Since its original publication almost 20 years ago, the Synonym Finder has
met with huge success among students, authors, speechwriters, and others in
search of le mot juste. (acceptable) [In this sentence, "since" is used to
modify the whole phrase "its original publication almost 20 years ago," not
the phrase "almost 20 years ago."]
反对since [a period of time] ago的书籍:
1992年的Collins Cobuild English Usage, p35.
2003年的Common Errors in English (by Dennis James Le Boeuf et al.), p19.
2004年新版的Collins Cobuild English Usage, p15.
赞成since [a period of time] ago的书籍:
1995年第二版Practical English Usage (by Michael Swan), p30.
不过2005年第三版和2016年第四版，作者把赞成的文字和例句全部删除。
https://reurl.cc/5vGd2q
I think the answer is this:
Yes, it is perfectly grammatical to say: The statue has stood there since 500
years ago.
No, it's not something a native English speaker would often say, as there is
the more natural (and shorter) alternative: The statue has stood there for
500 years.
However, you will very often find it where an event comes after the word
"since", as in: The statue has stood there since the battle 500 years ago.
https://www.usingenglish.com/forum/threads/since-ago.277590/
1. I haven’t seen Ali since two minutes ago.
2. I haven't been to London since two years ago.
The time frame is a period starting from a point in time (two years ago)
leading up to the present moment.
Both sentences are grammatical. However, a native speaker is more likely to
use the time expression ... for two years.