Fuel economy is an expression of what?

Answer: A — Miles driven per gallon of gasoline.

Fuel economy is primarily expressed as how many miles a vehicle can travel on a gallon of gasoline. This measurement can provide insight into the efficiency of a vehicle; when a car has a higher miles-per-gallon rating, it indicates that the vehicle uses fuel more efficiently, allowing drivers to travel further distances with less frequent refueling. This metric is crucial for consumers when assessing a car's performance, as it directly relates to operating costs and environmental impact. By considering the other options, it's clear that they frame fuel economy in ways that do not accurately describe its common representation. Gallons used per mile traveled describes fuel consumption efficiency but is not the standard way that fuel economy is presented. Likewise, dollars spent per gallon or per mile focuses more on the cost aspect rather than the efficiency measurement, which is not the traditional definition of fuel economy. Therefore, the first option correctly conveys the conventional understanding of fuel economy.