The correct answer is Option C.
Antonym means a word that is opposite in meaning to the given word.
In the given question, VACILLATION means indecision, uncertainty and inconsistency.
Thus the opposite of this word will be CONSISTENCY which means stability, consistency and regularity.
The remaining options are incorrect because:
Amplification means increasing the volume.
Stimulation means encouraging something to become active.
Eradication means destroying something completely.