I believe it is B. If not, I deeply apologize.
Explanation -
However :
Sarah has red hair. However, Mikayla doesn't.
Or :
It is either white or black. (Not used to show contrast)
But :
Ezra has a bike, but Mike doesn't.
Yet :
Cedric hasn't started his test. Yet, other people have already finished.
All of them are used to show contrast, but "Or" doesn't. Therefore, it is B.