which car has the greatest efficiency?

A 900 kg car that travels 20 km per liter of fuel
A 900 kg car that travels 15 km per liter of fuel
A 1200 kg car that travles 20 per liter of fuel
A 1200 kg car that travles 15 per liter of fuel

The car with the greatest efficiency is the one that travels the greatest distance per liter of fuel. In this case, it is the 900 kg car that travels 20 km per liter of fuel.