Final answer:
Siri uses artificial intelligence to function as a virtual assistant, interpreting and responding to user requests with technologies like voice recognition and machine learning.
Step-by-step explanation:
The piece of software from the options provided that is using artificial intelligence is d. Siri. Siri is a virtual assistant that is part of Apple's operating systems. It uses voice recognition, natural language processing, and machine learning to understand and respond to a wide variety of user requests. Examples include setting reminders, sending messages, and answering questions. In contrast, Microsoft Word, Photoshop, and Excel, while sophisticated software programs, do not incorporate advanced artificial intelligence to interact with users or learn from their behavior in the way Siri does.