瞒着

wǒ kěn dìng tā yǒu shén me shì mán zhe wǒ

我肯定她有什么事瞒着我。

I'm sure she's keeping something back from me.

wǒ jiù zhī dào tā zài mán zhe shén me

我就知道他在瞒着什么。

I knew he was hiding something.