Amazon Lex is the correct service because it provides advanced deep learning functionalities of automatic speech recognition (ASR) for converting speech to text, and natural language understanding (NLU) to recognize the intent of the text, enabling developers to build applications with highly engaging user experiences and lifelike conversational interactions. While Amazon SageMaker is an extensive machine learning service, it is not tailored specifically for creating chatbots. Amazon Comprehend is primarily used for text analysis to find insights and relationships in text, not for building chatbots. Amazon Kendra is an enterprise search service and does not focus on chatbot functionalities.