The correct tasks that the cluster manager performs in an indexer cluster are A. Generates and maintains the list of primary searchable buckets, B. If Indexer Discovery is enabled, provides the list of available peer nodes to forwarders, and D. Distributes app bundles to peer nodes. According to the Splunk documentation1, the cluster manager is responsible for these tasks, as well as managing the replication and search factors, coordinating the replication and search activities, and providing a web interface for monitoring and managing the cluster. Option C, ensuring all peer nodes are always using the same version of Splunk, is not a task of the cluster manager, but a requirement for the cluster to function properly2. Therefore, option C is incorrect, and options A, B, and D are correct.
1: About the cluster manager 2: Requirements and compatibility for indexer clusters

The Splunk Universal Forwarder is the only Splunk Enterprise offering that has its own license. The Splunk Universal Forwarder license allows the forwarder to send data to any Splunk Enterprise or Splunk Cloud instance without consuming any license quota. The Splunk Heavy Forwarder does not have its own license, but rather consumes the license quota of the Splunk Enterprise or Splunk Cloud instance that it sends data to.
The Splunk Cloud Forwarder and the Splunk Forwarder Management are not separate Splunk Enterprise offerings, but rather features of the Splunk Cloud service. For more information, see [About forwarder licensing] in the Splunk documentation.

Explanation/Reference: https://docs.splunk.com/Documentation/Splunk/7.3.1/Indexer/Configurethepeerindexes

Of the following types of files within an index bucket, the rawdata file type may consume the most disk. The rawdata file type contains the compressed and encrypted raw data that Splunk has ingested. The rawdata file type is usually the largest file type in a bucket, because it stores the original data without any filtering or extraction. The bloom filter file type contains a probabilistic data structure that is used to determine if a bucket contains events that match a given search. The bloom filter file type is usually very small, because it only stores a bit array of hashes. The metadata (.data) file type contains information about the bucket properties, such as the earliest and latest event timestamps, the number of events, and the size of the bucket. The metadata file type is also usually very small, because it only stores a few lines of text. The inverted index (.tsidx) file type contains the time-series index that maps the timestamps and event IDs of the raw data. The inverted index file type can vary in size depending on the number and frequency of events, but it is usually smaller than the rawdata file type