The composer of the opera "The Zoo" has composed how many major orchestral works?
The Zoo: The Zoo is a one-act comic opera, with music by Arthur Sullivan and a libretto by B. C. Stephenson, writing under the pen name of Bolton Rowe. Arthur Sullivan:  His works include 23 operas, 13 major orchestral works, eight choral works and oratorios, two ballets, incidental music to several plays, and numerous hymns and other church pieces, songs, and piano and chamber pieces.
13