Why does the Audi A3 have such impressive fuel efficiency?

I've heard great things about the Audi A3's fuel efficiency. Can anyone explain what makes it so efficient compared to other cars in its class?

The A3 also features an aerodynamic design and a lightweight body, which helps improve its fuel efficiency by reducing drag and improving overall performance.

In addition to its advanced engine technology, the A3 is also equipped with a regenerative braking system that captures energy from braking and stores it for later use. This helps improve fuel efficiency and reduce emissions.

The Audi A3 is equipped with a start-stop system that helps reduce fuel consumption by automatically turning off the engine when the car is stopped and restarting it when you release the brake pedal.