What is the BEST definition of elasticity in economics?

A. Elasticity of supply measures how the amount of a good changes when the producer hires more employees.
B. Elasticity of supply measures hot the amount of a good changes when the producer uses new materials.
C. Elasticity of demand measures how the amount of a good changes when it’s price goes up or down.
D. Elasticity of demand measures how the amount of a good changes when it’s distribution expands.