Why is the Audi A2 considered one of the most fuel-efficient cars?

I've heard that the Audi A2 is very fuel-efficient. Can you explain why this is the case?

The Audi A2 is equipped with an innovative lightweight aluminum body, making it significantly lighter than other cars in its class. This reduces the amount of energy needed to propel the car, resulting in better fuel efficiency.

In addition to its lightweight design, the Audi A2 also comes with advanced engine technology such as direct fuel injection, which helps to maximize fuel efficiency.

The Audi A2 also features a start-stop system, which automatically shuts off the engine when the car is at a standstill, reducing fuel consumption and emissions.