According to paragraph 4, what does Hockney argue the use of the camera obscura in producing art? A. Works produced using a camera obscura do not deserve as much respect as those produced without it. B. The camera obscura was probably used primarily as a training device, rather than used in producing finished works. C. Use of the camera obscura by Western art's great masters was probably relatively rare. D. While the use of the camera obscura may have helped artists, thy still needed to have significant artistic ability.