I am making an energy efficiency calculator for a fleet of vehicles. For
each year, make and model, I have specific information as to MPG, CO2, and
Air Pollution Score. I am trying to make a drop down list to choose year,
then based on year, makes that were purchased that year, then based on makes,
the models bought in that year of that make.

Each vehicle will have a row with columns: Year, Make, Model, MPG, Air
Quality. MPG and Air Quality be hard numbers, not selected in the drop-down.

Thank you for your help!