If a Member of Congress Has a Personal Interest in the Outcome

If a member of Congress has a personal interest in the outcome of a vote are they allowed to support it on the floor?

A) Yes, but there will be political costs and they may not be reelected
B) No, the parliamentarian will revoke their right to vote
C) No, the conflict-of-interest provision in the congressional rules prohibits it
D) No, the political parties prohibit their members from doing so