You've made some serious mistakes.

你犯了一些非常严重的错误。

He hasn't made any serious mistakes that I know of.

根据我所知，他没犯过什么严重错误。

For young leaders, this is essential, to avoid serious mistakes.

对年轻的领导者来说，这是避免犯下重大错误的关键。

What were the most serious mistakes you made in our negotiations?

在我们的谈判练习中，你所犯下最严重的错误是什么？

What were the most serious mistakes you made in your negotiations?

在我们的谈判练习中，你所犯下最严重的错误是什么？