Why can’t the question “what is art” ever really be answered

In contour drawing crossing lines is one way to indicate this

Brancusi's well-known sculpture of a bird was intended to a. display the physical qualities of a bird. b. emphasize the relative size of birds to humans. c. show the calming attributes of birds. d. emphasize the graceful qualities of a bird. select the best answer from the choices provided a b c d

What were some of the characteristics of renaissance art?