title: A great question.
mesh_terms: D002621:Chemistry / Q000266:history*; D049673:History, 20th Century; D049674:History, 21st Century; D010825:Physics / Q000266:history; D014508:Urea / Q000138:chemical synthesis / Q000737:chemistry; D014805:Vitamin B 12 / Q000138:chemical synthesis / Q000737:chemistry
chemical_list: D014508:Urea; D014805:Vitamin B 12