seriously

I'm speaking seriously; you really need to reconsider your decision to quit.

(Chinese) 我是认真说的；你真的需要重新考虑你辞职的决定。

The boss took the employee's complaints very seriously and promised an investigation.

(Chinese) 老板非常认真地对待员工的投诉，并承诺进行调查。

Seriously? You're actually going to run a full marathon without any training?

(Chinese) 真的吗？你真的打算在没有任何训练的情况下跑完一整场马拉松？

He told me he won the lottery, but I asked him 'Seriously?' because he's a joker.

(Chinese) 他告诉我他中了彩票，但我问他“真的吗？”，因为他爱开玩笑。