Which of the following is true of U.S. political parties since 1980?
I. Party bosses and party machines dominate national elections.
II. Superdelegates act alone to choose party nominees.
III. Third-party candidates have influenced the outcome of elections.
IV. National conventions help attract attention to the party platforms.

A. I only
B. I and II
C. III and IV
D. I, III, and IV
E. II, III, and IV