How was voter turnout essential to the outcome of the 2012 U.S. presidential election?

a. Republicans boosted the participation rates of their traditional voters and pushed voter registration for those favorably disposed to the Republican Party, while the Democrats paid less attention to grassroots work, concentrating instead on television advertising.
b. Democrats boosted the participation rates of their traditional voters and pushed voter registration for those favorably disposed to the Democratic Party, while the Republicans paid less attention to grassroots work, concentrating instead on television advertising.
c. Democrats boosted the participation rates of their traditional voters, while the Republicans pushed voter registration for those favorably disposed to their party and concentrated on television advertising.
d. Democrats boosted the participation rates of their traditional voters and TV advertising, while the Republicans concentrated on grassroots efforts.

b