How does the Audi A2 achieve such high fuel efficiency?

I've heard that the Audi A2 is one of the most fuel efficient models in its class. I'm curious to know how it is able to achieve such impressive fuel efficiency numbers.

The Audi A2 utilizes advanced lightweight materials and aerodynamic design to reduce weight and drag, resulting in improved fuel efficiency.

In addition to its efficient engine, the Audi A2 also utilizes regenerative braking technology to capture and store energy that would otherwise be lost during braking.

The Audi A2 also features an intelligent start-stop system that automatically turns off the engine when the vehicle is stopped, further improving fuel efficiency.