The answer is B. Manifesto.
A manifesto is a public declaration of principles and intentions, especially one issued before an election by a political party or other group.
A ballot is a piece of paper or other material on which voters mark their choices in an election.
An election is a formal process by which a vote is held to elect a person or group of people to a position of authority.
A vote is a formal expression of an opinion or choice, typically given in response to a question or proposal.
The word that is different from the rest is manifesto. The other three words are all related to the process of voting, while a manifesto is a document that outlines the principles and intentions of a political party or other group.