The correct option is C Whip
A whip is an official of a political party appointed to maintain parliamentary discipline among its members, especially so as to ensure attendance and voting in debates. Hence, Option C is correct. Among the rest of the options, statesman means skilled, experienced, and respected political leader or figure, diplomat means an official representing a country abroad, defector means a person who has abandoned their country or cause in favour of an opposing one. These options do not express this meaning, hence incorrect.