Consider the graphs in Figure 1, Polarization of the U.S. Congress, in the tutorial. What effect has the data shown in the graphs had on bipartisanship? a.) Since the 1970s, it has become easier for the political parties to compromise. b.) Bipartisanship has decreased since the 1970s. c.) Bipartisanship has been unaffected by the data shown in the graphs. d.) Bipartisanship has increased since the 1970s