While it’s true that C. Speech-to-Text is used to interpret what is spoken and convert it into text, and B. Key Phrase Extraction can process the text to identify the main points, these two alone might not be sufficient for a complete AI solution that controls smart devices using verbal commands. it doesn’t necessarily understand the context or the specific actions that need to be taken based on those key phrases. For example, in a command like “Turn on the living room lights”, key phrase extraction might identify “turn on”, “living room”, and “lights” as key phrases, but it doesn’t inherently understand that “turn on” is an action that needs to be applied to the “living room lights”. That's my reason why language modeling is a better answer than key phrase extraction.