Your answer is C. I can't really give much of a explanation for this one sorry. But I do hope this helps you.
B: Oxymoron is the answer.
When he either rescues her or kills the dragon
I believe that the closest synonym for the word overwhelmed is awestruck. It isn't jubilant, because that means happy. And overwhelmed isn't necessarily happy, it is just a strong emotion. Flattered and gracious just don't fit here.