He whirled round in a trice, with a revolver in his hand.

Answer: Option C

Circle : a round plane figure whose boundary (the circumference) consists of points equidistant from a fixed point (the centre).
Trifle : a thing of little value or importance.
Instant : prepared quickly and with little effort.
Hurry : move or act with great haste.
Trice : in a moment; very quickly.

Synonym of Trice is Instant