Final answer:
To manage and monitor data security on a Hadoop platform, Apache Ranger is the appropriate tool among the given options, as it specializes in centralized security administration for various Hadoop components.
Step-by-step explanation:
If you need to monitor and manage data security across a Hadoop platform, the most suitable tool to use would be A) Ranger. Apache Ranger offers a comprehensive platform for security policy management across the Hadoop ecosystem. This includes fine-grained access control and centralized security administration for Hadoop components such as HDFS, HBase, Hive, and others. While Sentry, Atlas, and Knox are also part of the Hadoop security ecosystem, Ranger is specifically tailored towards security monitoring and management. Sentry provides a system for enforcing fine-grained, role-based authorization to data and metadata stored on a Hadoop cluster. Atlas is more focused on data governance and metadata management, and Knox is a gateway service that provides secure access to the Hadoop cluster's REST APIs and UIs.