Two Single Select

Content

I have 2 Single Select next to each other. I want to achieve following use case.

 

if user does select value in select-single A then select-single B is disabled.

If user does not select any value in select-single A then select-single B is enabled for selection.  If user goes ahead and selects value in B then Select-single A should be disabled.

what is the best way to implement this scenario ?