Copper is a good conductor of electricity. Copper mixed with silver is expensive. Copper can be pounded into many shapes. Copper is an excellent conductor of heat.
I gave my students this multiple choice question: Which statement is an opinion about the element copper?

Only one answer is correct among these 4 choices:
- Copper is a good conductor of electricity.
- Copper mixed with silver is expensive.
- Copper can be pounded into many shapes.
- Copper is an excellent conductor of heat.

Could you tell me which one is correct?

Copper mixed with silver is expensive.