✔ 最佳答案
1.) before Monday v. by Monday
Please turn in this assignment before Monday. (星期一之前,準確一點是星期日23:59:59 前)
Please turn in this assignment by Monday. (星期一當天結束前,如果你是上班族,by Monday 指下班前)
2.) by December (12月31日結束前)
We'll be out of the EU by December 2018, says new Brexit Secretary David Davis as he calls for 'brisk' approach to negotiations... (2018 December 31 結束前,也就是 before 2019)
before December = by November
[補充]
上面說的是原則。實際運用上,須考慮不同情況對 "截止時間" 的解釋不同。
例如 Please turn in this assignment by Monday. 如果是老師對學生作業的要求,通常是指星期一上課時交。當然現在很多老師採用email,或是upload 到clouds,所以時間上更彈性,一天24小時都可接收。