Which of the following is a physical change?
-burning
-rusting
-freezing
-oxidation

Freezing is a physical change caused by temperature. 
The others cannot be undone easily, because the chemical structure has changed.

The statement that best explains why heating a liquid affects its viscosity is that "The molecules move faster at higher temperatures and overcome attractions more easily.". Remember that viscosity is a physical property of the fluids that measure the resistance (opposition) to flow and it, generally decreases, as the temperature increases and the intermolecular force decrease.