a ruler a balance a compass a protractor
I gave my students this multiple choice question: A student plans to measure the thermal expansion of a strip of metal as it is heated from 0ºC to 50ºC. Which piece of equipment should he use to measure the expansion?

Only one answer is correct among these 4 choices:
- a ruler
- a balance
- a compass
- a protractor

Could you tell me which one is correct?

a ruler