"Submissive" means ready to conform to the authority of others; meek, obedient, or docile.
Checking options:
- (a) Obstinate → opposite (stubborn).
- (b) Unyielding → opposite of submissive.
- (c) Stubborn → opposite meaning.
- (d) Docile → correct synonym, meaning obedient and easily managed. \[ \boxed{\text{Docile}} \]