repeat the investigation change the volume of water add more salt to the mixture do the investigation without salt
I gave my students this multiple choice question: A student is measuring the boiling point of a salt and water mixture. He takes one temperature measurement of 105°C. Which is the best way to ensure the results are valid?

Only one answer is correct among these 4 choices:
- repeat the investigation
- change the volume of water
- add more salt to the mixture
- do the investigation without salt

Could you tell me which one is correct?

repeat the investigation