What Best Represents the Trend of Party Polarization Over the Last

What best represents the trend of party polarization over the last three decades?

A) The parties have become less polarized because more and more voters are opting to become independents.
B) Both Republicans and Democrats have become more liberal.-
C) While members of Congress have not become more extreme,ordinary citizens have.
D) Each congressional party has become more homogeneous,and the distance between parties has increased.