Answer
The interval level.
Work Step by Step
The differences between years of birth have meaning; if the year of birth of the student A is 1995 and the year of birth of the student B is 1997, it means that student B is 2 years younger than student A. Notice that, the year 2000 is not the double of the year 1000 because the world has begun billions of years ago and the year 0 is not the beginning.
