The correct answer is C. The political party function that involves it selling its candidate is to run a political campaign.
A political campaign is an organized effort carried out to influence the decision of an electoral process in a specific group of voters, which may be that of a city, state or country, or to a certain sector of the population. In democracies, campaigns often refer to electoral campaigns where representatives are chosen or a referendum is decided. A political campaign also includes efforts to alter the policy or ideology of any institution.