Final answer:
The mid-19th century opera scene was dominated by star singers and virtuoso performers who drew large audiences, influenced by the star system and the growing middle class.
Step-by-step explanation:
By the mid-19th century, the key draw for audiences of opera productions were star singers and virtuoso performers. This was largely due to the star system, which had emerged as a trend in the theatre where exceptional actors and musicians became significant attractions for the audiences. This period saw the rise of a bourgeois class that greatly expanded the audience size for public concerts and operas, giving more emphasis on performers capable of captivating large audiences. Operas at that time featured the works of Romantic composers like Wagner, who created intricate and emotive music that required highly skilled singers to execute. Thus, the answer to the question is D) Star singers and virtuoso performers.