The Knockout way to apply a class to a specific button when clicked

Hi and thanks for reading!

I have 3 buttons, that are answers in a multiple choice exam simulator,i wanna apply a red background color only to the clicked answer (the green color background logic for the right one no matters , I have resolved).

How i do that in knockout?

I have read here that the right way is do a data-bind click, and change an observable...And then apply a class to the button depending of the value of it...But i have three button, and if i do this in the three buttons, the three gonna be red...So..What D:?

Thanks.