Which of the following is NOT a cluster manager for Spark?

Hadoop is not a cluster manager for Spark; rather, it is a framework that allows for the distributed processing of large data sets across clusters of computers using simple programming models. The Hadoop ecosystem includes its own cluster management features, primarily through YARN (Yet Another Resource Negotiator), which can manage resources for various applications including Spark.

In contrast, YARN, Mesos, and Spark's standalone cluster mode are specific cluster managers that facilitate the deployment and resource allocation for Spark applications. YARN, for example, allows different applications to share the resources of a cluster, while Apache Mesos provides a more general framework for resource scheduling, and Spark's standalone cluster mode is a simple setup where Spark manages resources itself without needing an external cluster manager.

Thus, identifying Hadoop as the option that is not a cluster manager for Spark is accurate, as it serves a different purpose within the broader ecosystem of big data processing.