Dramatic performances, often accompanied by music, were popular in the markets. The actors were distinguished in rank by type and color of clothing, honing their acting skills at drama schools. Satirical sketches denouncing corrupt government officials were especially popular. Actors on stage always spoke their lines in Classical Chinese; vernacular Chinese that imitated the common spoken language was not introduced into theatrical performances until the subsequent Yuan dynasty. Although trained to speak in the erudite Classical language, acting troupes commonly drew their membership from one of the lowest social groups in society: prostitutes. Of the fifty some theatres located in the pleasure grounds of Kaifeng, four of these theatres were large enough to entertain audiences of several thousand each, drawing huge crowds which nearby businesses thrived upon.