https://docs.splunk.com/Documentation/Splunk/9.0.0/DistSearch/Distributedsearchgroups

A bucket is the object that stores events inside of an index. According to the Splunk documentation1, "An index is a collection of directories, also called buckets, that contain index files. Each bucket represents a specific time range." A bucket can be in one of several states, such as hot, warm, cold, frozen, or thawed1. Buckets are managed by indexers or clusters of indexers1.

The correct answer is D. Place both props . conf and transforms . conf on the Heavy Forwarder for source A, and place both props . conf and transforms . conf on the indexer for source B.
According to the Splunk documentation1, to mask sensitive data from raw events, you need to use the SEDCMD attribute in the props.conf file and the REGEX attribute in the transforms.conf file. The SEDCMD attribute applies a sed expression to the raw data before indexing, while the REGEX attribute defines a regular expression to match the data to bemasked.You need to place these files on the Splunk instance that parses the data, which isusually the indexer or the heavy forwarder2. The universal forwarder does not parse the data, so it does not need these files.
For source A, the data is routed through a heavy forwarder, which can parse the data before sending it to the indexer. Therefore, you need to place both props.conf and transforms.conf on the heavy forwarder for source A, so that the masking takes place before indexing.
For source B, the data is routed directly to the indexer, which parses and indexes the data. Therefore, you need to place both props.conf and transforms.conf on the indexer for source B, so that the masking takes place before indexing.
References:1:Redact data from events - Splunk Documentation2:Where do I configure my Splunk settings? - Splunk Documentation

Indexers, search head, deployment server, license master, universal forwarder. This is the combination of Splunk component instances that are needed to handle the volume of data from collecting log files from 50 Linux servers and 200 Windows servers, following the best practices. The roles and functions of these components are:
Indexers: These are the Splunk instances that index the data and make it searchable. They also perform some data processing, such as timestamp extraction, line breaking, and field extraction. Multiple indexers can be clustered together to provide high availability, data replication, and load balancing.
Search head: This is the Splunk instance that coordinates the search across the indexers and merges the results from them. It also provides the user interface for searching, reporting, and dashboarding. A search head can also be clustered with other search heads to provide high availability, scalability, and load balancing.
Deployment server: This is the Splunk instance that manages the configuration and app deployment for the universal forwarders. It allows the administrator to centrally control the inputs.conf, outputs.conf, and other configuration files for the forwarders, as well as distribute apps and updates to them.
License master: This is the Splunk instance that manages the licensing for the entire Splunk deployment. It tracks the license usage of all the Splunk instances and enforces the license limits and violations. It also allows the administrator to add, remove, or change licenses.
Universal forwarder: These are the lightweight Splunk instances that collect data from various sources and forward it to the indexers or other forwarders. They do not index or parse the data, but only perform minimal processing, such as compression and encryption. They are installed on the Linux and Windows servers that generate the log files.