Knockback (support gem) and King of the Hill (passive) interaction

Hi guys, i have a question.
Is the knockback from the support gem overlapping the knockback on crit from the King of the Hill passive?

How do they interact?

Lets say i have:

50% chance to knockback from support gem
50% critical chance (with 100% chance to knockback on crit)

Do they:

A. stack, giving me 100% chance to knockback on hit?
B. wait in line, first checking if i crit, if not then roll the dice on 50% knockback chance from support gem, giving me basically 75% chance to knockback
C. completely overlap, giving me a 50% chance to either crit, either knockback, either both, either none?

It's B.