C

Step 1: Understand the properties of materials used in springs.
Step 2: Elasticity is the ability of a material to return to its original shape after deformation. In general, metals have different elastic properties.
Step 3: When comparing steel and copper, steel is generally more elastic than copper, which means it can undergo deformation and still return to its original shape more effectively. This makes it more suitable for applications requiring repeated stress and strain, like springs.
Step 4: Although copper has good ductility and can conduct electricity, it is not as advantageous as steel in terms of elasticity and strength.
Therefore, the best option is C: Steel is more elastic than copper.