Recent Polarization Between the Democrats and Republicans in the United

Recent polarization between the Democrats and Republicans in the United States is surprising to sociologists because political theory predicts that:

A) two-party systems often lead to similarity between the parties because the big "middle" is where the votes are
B) alternative parties such as the Green Party and the Libertarian Party would produce a robust multiparty system
C) each party contains radical alternatives that, surprisingly, are being suppressed in favor of a watered-down common ground
D) coming together is more likely than polarizing because mainstream parties share so much common ground in concern for security, public goods, and human welfare