Here's a problem to solve: 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?

Among the 4 following options, which is the correct answer?

- A: repeat the investigation
 
- B: change the volume of water
 
- C: add more salt to the mixture
 
- D: do the investigation without salt
 