Synonym of UNDULATE

Answer: Option C

Retard : delay or hold back in terms of progress or development.
Decrease : make or become smaller or fewer in size, amount, intensity, or degree.
Wave : move one's hand to and fro in greeting or as a signal.
Flood : an overflow of a large amount of water beyond its normal limits, especially over what is normally dry land.
Undulate : move or go with a smooth up-and-down motion.

Synonym of Undulate is Wave