ago
/əˈgəʊ/adverb
- before the present; earlier (used with a measurement of time)以前; 更早（与表示时间长度的词连用）：
he went five minutes ago
他五分钟前走的
as long ago as 1942
早在1942年以前
not long ago.
不久前。
USAGE
When ago is followed by a clause， the clause should be introduced by that rather than since, e.g. it was sixty years ago that I left this place （not it was sixty years ago since I left this place ）. The use of since is not correct in standard English.
词源
Middle English ago, agone, past participle of the obsolete verb ago 'pass'， used to express passage of time.