Answer: Nominal
Explanation:
When the Nominal measurement scale is used, it means the data was sorted into labels or names which is why it is sometimes referred to as Named data. For instance, sorting dogs in a park into their species i.e Husky, American Bull, German Shephard etc.
There is no quantitative value and usually there is no ordering method to this measurement scale.
The professor sorted her students according to their majors which in this case acted as labels so the Professor was using the Nominal measurement scale.