英文文法一問～～PLZ～句子上文法?

Moreover , there is also an increased possibility of them making mistakes when working overtime ,
此外，超時工作令他們犯錯的可能性增加，

「which could have been avoided had they completed the same tasks during normal working hours in the daytime.」
這原是可以避免的，要是他們在白天正常工作時間內完成同樣的工作。

= had they completed the same tasks during normal working hours in the daytime, these mistakes could have been avoided.
= If they had completed the same tasks during normal working hours in the daytime, these mistakes could have been avoided.
這時，你可看出這是標準的 "與過去事實相反"的假設語法。原句中的 which 指 mistakes

which 是 主要句裡面的 mistakes 的關係代名詞. 所以,你在括號裡的 是一個<關係子句>
<had they complete...in the day time> 是<假設語氣> = if they had completed ... in the day time.
所以 你的問題子句 = The mistakes could have been avoided if they had completed the same tasks ... in the day time.

意思是: 這些錯誤 若是 是在正常白天工時 裡做的話 就不會發生的

notes:
1. 這英語寫得不好 犯規的地方很多
2. 正規地說 possibility 是用錯了 應該使用probability 或是 chance
3. 整句話 <代名詞>太多了,尤其是 they/them 的使用 都很糟糕 是應該避免的
你先自己想想看 為神 再加入討論吧!

> Thx so much , 如果整句改，你會如果改～？
I would put it this way:

Moreover, working overtime increases the chance of making mistakes which could have been avoided had the same tasks been completed during the regular work hours in the daytime.