What Is the Underlying Idea Behind the Coattail Effect

What is the underlying idea behind the coattail effect?

A) Voters tend to support congressional candidates in the party opposite their selection for president.
B) Voters pay more attention to all aspects of an election when the president is on the ballot.
C) Voters will turnout in higher numbers, which boosts a congressional candidate's chances of election.
D) Voters will select congressional candidates based on who they selected for president.