freedom from labor itself is not new; it once belonged among the most firmly established privileges of the few. in this instance, it seems as though scientific progress and technical developments had been only taken advantage of to achieve something about which all former ages dreamed but which none had been able to realize.

something about다음에 what이 아니라 which를 쓴 이유가 뭔가요?전치사 about의 목적어가 나오려면 about 뒤에 명사구가 와야되는데 그럴려면,dreamed의 목적어 역할까지하는 관계대명사 what이 나와야되는거 아닙니까?만약 저 본문처럼 which를 쓰고싶으면 선행사가 앞에 나와줘야되는데 본문엔 선행사가 없잖아요.
답변부탁드립니다.