Most of the staff is restive under the new manager's rule.

Answer: Option D

Relaxed : free from tension and anxiety.
Friendly : kind and pleasant.
Uneasy : causing or feeling anxiety; troubled or uncomfortable.
Obstinate : stubbornly refusing to change one's opinion or chosen course of action, despite attempts to persuade one to do so.
Restive : (of a horse) stubbornly standing still or moving backwards or sideways; refusing to advance.

Synonym of Restive is Obstinate