Duchamp was an innovative French-American artist who influenced the Dada, Surrealist, and Pop art movements. His irreverence for conventional aesthetic standards led him to exhibit commonplace objects as works of art that he called “ready-mades,” intended as a derisive gesture against the excessive importance attached to works of art. His most famous works include the controversial Cubist-Futurist painting Nude Descending a Staircase and Fountain, which features what object? Discuss