Correct Answer: D
Explanation:
Meaning: Vacillate means to waver back and forth, unable to decide.
To waver in mind or opinion, to oscillate or fluctuate.
Example: It seems like you vacillate between 10 and 20 members at any given time.
Synonyms: Fluctuate, Dither, Waver, Change, Stagger
Antonyms: Remain, Stay, Hold, Persist