(c) Natural Language Processing (NLP)
Voice assistants like Siri and Alexa take natural speech, process it, and execute tasks — this is done using Natural Language Processing (NLP).
The passage explicitly states: "Hey Alexa, play some music" and "Hey Siri, what's the weather today" as examples of Voice Assistants, listed under Applications of Natural Language Processing. NLP enables machines to understand and respond to human speech. ML is a broader domain; CV deals with images; "Technical Vision (TV)" does not exist as an AI domain.