Which of the following represents a physical change in matter?
a).combustion of carbon to form carbon dioxide
b).rusting
c).melting a stick of butter
d).seperating hydrogen gas from water

Johannesburg kepler, an apprentice of brahe, believed in the heliocentric universe but rejected past astronomers belief in

When does the circulatory system work with the respiratory system? a. during blood cell formation b. during cellular respiration c. during intestinal digestion d. during a viral infection

For a comparative or experimental investigation, scientists often make a testable about a scientific question, and then they test it in the investigation. a.control b.hypothesis c.procedure d.system