Amazon Kendra is an intelligent search service powered by machine learning. Its primary function is to enable users to search for information across various content repositories. Kendra can connect to data sources, including Amazon S3, to index documents and their content. It then provides a natural language search capability, allowing users to find specific text within those documents. This directly fulfills the company's requirement to search for text in documents stored in Amazon S3.

B. Amazon Rekognition is an image and video analysis service. While it can detect text in images, it is not a document search service.
C. Amazon Polly is a text-to-speech service that converts written text into lifelike speech; it does not perform search operations.
D. Amazon Lex is a service for building conversational interfaces, such as chatbots, and is not designed for searching document repositories.

1. Amazon Kendra Developer Guide: In the "What is Amazon Kendra?" section, the documentation states, "Amazon Kendra is an intelligent search service powered by machine learning (ML)... so your employees and customers can easily find the content they are looking for... scattered across multiple locations and content repositories". It explicitly lists Amazon S3 as a supported data source. (Source: AWS Documentation, Amazon Kendra Developer Guide, "What is Amazon Kendra?", Section: "How it works").

2. Amazon Rekognition Developer Guide: The "What Is Amazon Rekognition?" section describes the service as one that "makes it easy to add image and video analysis to your applications." This confirms its purpose is analysis, not document search. (Source: AWS Documentation, Amazon Rekognition Developer Guide, "What Is Amazon Rekognition?", First paragraph).

3. Amazon Polly Developer Guide: The "What Is Amazon Polly?" section states, "Amazon Polly is a service that turns text into lifelike speech." This clarifies its function is text-to-speech conversion. (Source: AWS Documentation, Amazon Polly Developer Guide, "What Is Amazon Polly?", First paragraph).

4. Amazon Lex V2 Developer Guide: The "What is Amazon Lex?" section explains, "Amazon Lex is an AWS service for building conversational interfaces for applications using voice and text." This defines its role in creating chatbots. (Source: AWS Documentation, Amazon Lex V2 Developer Guide, "What is Amazon Lex?", First paragraph).