What Best Explains the Demise of Party Machines

What best explains the demise of party machines?

A) congressional reforms that prevented private party meetings in "smoke-filled rooms"
B) Keynesian economic reforms that increased individual wealth
C) judicial reforms that ended the "pay to play" system of assigning public defenders -Consider This: Party machine weakened after it gave jobs based on the ability to perform the job.
D) progressive reforms that instituted a merit-based hiring system