Political parties in Congress ______.

A. have grown less unified over time, and there is less agreement on major votes and the ideological gap between the parties has shrunk
B. have grown more unified with higher levels of support on party unity votes as well as becoming more polarized along ideological lines
C. have witnessed the Democratic Party become more unified and more ideologically homogeneous while Republicans remain fractured into competing coalitions
D. have gotten much stronger in the House of Representatives while growing weaker and less ideologically polarized in the Senate

Answer: B