WRONG:Write the report until 5 pm.
RIGHT: Write the report by 5 pm.
Write the report until 5 pm means “Start writing the report now, continue writing it until 5 pm, then stop writing it regardless of whether it is finished or not.”
當你使用“until”意味著“從現在開始寫報告，一直寫，寫到下午五點，然後不管你寫沒寫完，都不能再寫了”。
Write the report by 5 pm means “Make sure that at 5 pm the letter is written and finished”.
當你使用“by”就表示“確保一定要在下午五點前寫完這封信”。
Use “by” when you refer to a deadline.
使用“by”，你指的是一個最後期限。
Use “until” when you refer to the period of time before a deadline.
使用“until”，你指的.是在最後期限之前的一段時間。
Here’s a summary:
總結：
1.I can do it by 5 pm.
我能在下午五點前做完。
2.I can do it until 5 pm.
我會做到下午五點(不管有沒有完成)。
3.I can’t do it by 5 pm.
下午五點前我做不完。
4.I can’t do it until 5 pm.
我要到下午五點才能開始做。
