how to remove specific character in string c#

Question

how to remove specific character in string c#

 

 

https://www.youtube.com/watch?v=_79dYUl-aEo?list=PL668E4AAB9C4CA96E&hl=en_US

 

 

i neeed out put: https://www.youtube.com/watch?v=_79dYUl-aEo  like this 

 

 

 

i know how to remove after question mark string but here i need to remove after second '? ' onwards plz help very soon