http://documents.saintleo.edu/docs/GBA334/GBA334_Group_Project_Guidelines.pdf
 
How does gas mileage depend on the [blank] of the vehicle? [Blank] could be weight, engine size, seating capacity, size (e.g. compact, sub-compact, SUV), etc. There should be multiple predictor variables included.
 
Variables: engine size, weight, car size