If a Third-Party Candidate Has No Expectation of Winning an Election

If a third-party candidate has no expectation of winning an election, what would be a positive reason for him/her to run for the presidential office?

A) To cast doubt on the legitimacy of the two major parties
B) To create doubts in the minds of citizens concerning the trustworthiness of government
C) To keep the successful major party from winning with a majority of the votes
D) To advocate for and raise awareness of a particular ideology or cause, and to garner support for the issue among voters
E) To advocate for overthrow of the two-party system in the United States