The level of measurement of years of education is c) interval ratio.
Years of education represent a quantitative measure where the number of years can be counted and compared. The interval ratio level of measurement means that the difference between the values is meaningful; for example, the difference between 12 and 16 years of education is the same as the difference between 8 and 12 years. Additionally, there is a true zero point (zero years of education, which means no education), which defines it as a ratio measurement. Therefore, years of education fall under the category of interval ratio measurement.