By the nineteenth century, the old patron system of the classical era had been replaced by a. ascap membership b. the public concert system c. academic tenure d. the religious scholastic system

In my opinion, the answer is B. the public concert system. Before that, performances were sponsored and held mainly in the rich patrons' mansions. Composers and performers earned their living thanks to their support. However, by the beginning of the 19th century, the era of commercial public concerts began. Composers could conduct their symphonies and other works in front of thousands of people (middle classes among them), in large concert halls. Even soloists held concerts (Franz Liszt being among the most notable and popular ones). The great concert piano appeared, such as we know today. 

The public concert system. Supporters of the arts are now composed more of the public masses through commercialization of the arts, such as public orchestra and theater performances which attempt to to gather revenue from tickets sold. Additional support is usually provided by non-profit foundations in support of the arts, as well as grants.