Arecent comprehensive study of the decline in political participation in the united states found that half of the drop-off could be accounted for by

The study found that half of the drop-off could be accounted for by : reduce mobilization effort 
mobilization effort refer to the cardiac works that has to be putted in order to do something. As people tend to be more secluded and relied on technology to do and get anything, people tend to be less interested to got up and walk to the voting booth

Ithink it would be choice b (county). hope this you!