Final answer:
The 'educational level' variable, measured in total years of school completed, is at the d) ratio level because it has a natural zero point which allows for the calculation of ratios.
Step-by-step explanation:
The variable 'educational level measured in total years of school completed' is measured at the ratio level. The ratio level of measurement is the highest form of measurement which signifies that the data has a natural zero point.
Permitting calculations of ratios. Consequently, years of education completed can not only be counted and ranked but can also be used to calculate meaningful ratios, such as saying someone with 16 years of education has twice as many as someone with 8 years.