AWS Glue is the correct service for transforming petabytes of unstructured data into a structured format suitable for machine learning tasks.

AWS Glue:

A fully managed extract, transform, and load (ETL) service that makes it easy to prepare and transform unstructured data into a structured format.

Provides a range of tools for cleaning, enriching, and cataloging data, making it ready for data scientists to use in ML models.

Why Option D is Correct:

Data Transformation: AWS Glue can handle large volumes of data and transform unstructured data into structured formats efficiently.

Integrated ML Support: Glue integrates with other AWS services to support ML workflows.

Why Other Options are Incorrect:

A. Amazon Lex: Used for building chatbots, not for data transformation.

B. Amazon Rekognition: Used for image and video analysis, not for data transformation.

C. Amazon Kinesis Data Streams: Handles real-time data streaming, not suitable for batch transformation of large volumes of unstructured data.