What Have Scholars Discovered About Voting Based on a Number

What have scholars discovered about voting based on a number of different field experiments?

A) telephone calls stressing the importance of voting increased turnout the most
B) television advertising about the closeness of the election had the greatest effect on turnout
C) personal visits combined with a message about the closeness of the election increased turnout the most
D) Americans have become so apathetic that there is very little that can be done to increase voter turnout above 50%