uncombined造句怎么写

"Arsenic: Nonmetallic to semimetallic chemical element, chemical symbol As, atomic number 33. It exists uncombined in two stable (and several unstable) allotropes, one gray and one yellow, But is more often found in nature as the sulfide or oxide."

"It probably does not occur uncombined in nature But is found in natural alloys with other noble (i.e., chemically inactive or inert) metals."

Hard metals--Metallographic determination of porosity and uncombined carbon

"Molybdenum : Metallic chemical element, one of the transition elements, chemical symbol Mo, atomic number 42. It is a silvery gray, relatively rare metal with a high melting point (4,730 f [2,610 c]) that does not occur uncombined in nature."