C is your Answer
I know this because...
In all elections, but especially in the case of congressional elections, the outcome of an election is often driven by factors and events beyond the control of the candidates and parties., Even strong candidates or incumbents can lose what might have been considered an easy win.
In congressional campaigns, campaign finance laws and constitutional provisions require particular attention; these, as well as the ungovernable factors of the political and economic climate, shape the way that candidates and their teams, as well as political scientists, must think about these elections.