Given the question: Given the following context:  After the Great War, Moore received an ex-serviceman's grant to continue his education and in 1919 he became a student at the Leeds School of Art (now Leeds College of Art), which set up a sculpture studio especially for him. At the college, he met Barbara Hepworth, a fellow student who would also become a well-known British sculptor, and began a friendship and gentle professional rivalry that lasted for many years. In Leeds, Moore also had access to the modernist works in the collection of Sir Michael Sadler, the University Vice-Chancellor, which had a pronounced effect on his development. In 1921, Moore won a scholarship to study at the Royal College of Art in London, along with Hepworth and other Yorkshire contemporaries. While in London, Moore extended his knowledge of primitive art and sculpture, studying the ethnographic collections at the Victoria and Albert Museum and the British Museum. The student sculptures of both Moore and Hepworth followed the standard romantic Victorian style, and included natural forms, landscapes and figurative modelling of animals. Moore later became uncomfortable with classically derived ideals; his later familiarity with primitivism and the influence of sculptors such as Constantin Brâncuși, Jacob Epstein, Henri Gaudier-Brzeska and Frank Dobson led him to the method of direct carving, in which imperfections in the material and marks left by tools became part of the finished sculpture. Having adopted this technique, Moore was in conflict with academic tutors who did not appreciate such a modern approach. During one exercise set by Derwent Wood (the professor of sculpture at the Royal College), Moore was asked to reproduce a marble relief of Domenico Rosselli's The Virgin and Child by first modelling the relief in plaster, then reproducing it in marble using the mechanical aid known as a "pointing machine", a technique called "pointing". Instead, he carved the relief directly, even marking the surface to simulate the prick marks that would have been left by the pointing...  answer the following question:  What form became the primary motif of Moore's sculpture?
The answer is:
the Chac Mool