6. What happens to the materials in the presence or absence of oxygen? A. burning of the materials C. change in the materials B. melting of the malerials D. materials remain the same 7. What is formed when metals are exposed to moisture? A. dust B. rusi C. heat D. fuel 8. Which of the following could cause fish kille A. lack of oxygen supply C. use of illegal fishing methods B. hot summer temperature D. lack of carbon dioxide supply 9. Which of the following factors influence the formation of rust on irone A. Increased level of oxygen C. dropping of oxygen B. moisture and oxygen D. oxygen level​