The correct option is
A To exult over a vanquished adversary
To “crow over” means to
Exult loudly about, especially over someone's defeat.“To exult over a vanquished adversary” means to show triumph and elation over a defeat(vanquish) against an opponent (adversary).
“To shrink to size” means to become small.
“To interdict” means a prohibition with authority.
“To bemoan” means to express discontent or sorrow.
“To grieve” means to express sorrow.
Hence option A is the correct meaning of the given phrase.