How does the Audi A4 achieve its impressive fuel efficiency?

I have heard that the Audi A4 has excellent fuel efficiency, especially for its class. Can you explain how this is achieved?

The Audi A4 utilizes a unique turbocharging system, called the Audi valvelift system, to optimize engine performance and reduce fuel consumption.

Additionally, the Audi A4 comes equipped with a start-stop system that automatically shuts off the engine when idling, reducing unnecessary fuel consumption.

The car also has a lightweight construction, with its body made primarily of aluminum, which helps to improve overall efficiency and handling.