What does it mean that photographs are two-dimensional?

Automobile fuel efficiency is often measured in miles that the car can be driven per gallon of fuel (mpg). heavier cars tend to have lower fuel efficiencies (lower mpg ratings). which variable (weight or fuel efficiency) is most naturally considered the explanatory (predictor) variable in this context?

Most short-period comets do not have randomly oriented orbits because

How much energy must a refrigerator absorb from 225 g of water so that the temperature of the water will drop from 35°c to 5°c