他瞒着我去旅行。
tā mán zháo wǒqù lǚxíng 。
He concealed from me that he went traveling.
你不应该瞒着她真相。
nǐ bù yīnggāi mán zháo tā zhēnxiàng 。
You shouldn't conceal the truth from her.
我知道你在瞒我什么。
wǒzhīdào nǐzài mán wǒ shénme 。
I know what you are concealing from me.