The most innovative period of Cubism was before 1914. After World War I, with the support given by the dealer Léonce Rosenberg, Cubism returned as a central issue for artists, and continued as such until the mid-1920s when its avant-garde status was rendered questionable by the emergence of geometric abstraction and Surrealism in Paris. Many Cubists, including Picasso, Braque, Gris, Léger, Gleizes, and Metzinger, while developing other styles, returned periodically to Cubism, even well after 1925. Cubism reemerged during the 1920s and the 1930s in the work of the American Stuart Davis and the Englishman Ben Nicholson. In France, however, Cubism experienced a decline beginning in about 1925. Léonce Rosenberg exhibited not only the artists stranded by Kahnweiler’s exile but others including Laurens, Lipchitz, Metzinger, Gleizes, Csaky, Herbin and Severini. In 1918 Rosenberg presented a series of Cubist exhibitions at his Galerie de l’Effort Moderne in Paris. Attempts were made by Louis Vauxcelles to claim that Cubism was dead, but these exhibitions, along with a well-organized Cubist show at the 1920 Salon des Indépendants and a revival of the Salon de la Section d’Or in the same year, demonstrated it was still alive.
In what year did Rosenberg refuse to exhibit Cubist works at Galerie de l’Effort Moderne? (If the question is unanswerable, say "unanswerable")
unanswerable