I believe the answer is “resignedly.”
Explanation:
The word choices “contemplated” and “sullenness” can be eliminated because they are not in the right tense, so the sentence would be grammatically incorrect. I would eliminate the answer “bewildered” because that implies that they are surprised to be grounded. “Resignedly” means “with resignation and acceptance,” which matches the tone of the sentence (AKA, defeated and ready for their consequence).