Final answer:
Pasteurization is the process used to extend the shelf life of beverages like milk and juice, with UHT pasteurization being a method that allows milk to be stored unrefrigerated for up to 90 days.
Step-by-step explanation:
The processing method used to extend the shelf life of beverages such as milk and juice is D. Pasteurization. This method involves heating milk or juice to a specific temperature to kill pathogens and reduce the number of microbes that cause food spoilage. UHT pasteurization is a type of pasteurization that subjects milk to ultra-high temperatures, around 140 °C for a few seconds, which effectively sterilizes it. This allows the milk to be sealed and stored for long periods without refrigeration, typically for up to 90 days.