In a beaker, sugar is dissolved in water, and then the water is heated and evaporates. The sugar is recovered, and heat is again applied. Vapor is released, and the material in the beaker changes from white to black. What must you know to determine if a chemical change occurred?

A) the boiling point of water

B) the boiling point of sugar

C) the identity of the black substance

D) temperature at which sugar evaporates