Build wordpress theme on top of Open source Theme

Hi everyone I hope you guys doing well.
I have a silly question? Can I build my WordPress theme**(commercially use)** on top of an open-source theme which you can find on WordPress Themes | repository and sell it on Themeforest. is that allowed?

And I’m sorry for my broken English

Thank you

No, you cannot sell the theme at ThemeForest - you will need an approval from the original theme author to be able to sell the same theme ( with modifications )