how about the following explanation on the usage of 'since' and

Chinese stock market continued to fall on Tuesday since three weeks before ... =
Chinese stock market continued to fall on Tuesday since the starting of the fall three weeks before the fall on Tuesday ...

Googled and found the following interesting on 'before', 'ago' and 'earlier':
http://www.italki.com/question/111799

所有跟帖： 

• 我記得，since當“自從”時， -beautifulwind- ♀ (223 bytes) () 07/30/2015 postreply 20:15:28

• 閱讀大家不同的翻譯版本收獲不小，尤其是幾位寫作大拿的，用詞和句法讓人眼前一亮。 -yingyudidida- ♂ (24 bytes) () 07/30/2015 postreply 20:16:49

• 嘿嘿，必須謝謝你的發明：） -beautifulwind- ♀ (0 bytes) () 07/30/2015 postreply 20:57:52