The Data Preview feature should be used when validating the parsing of data. The Data Preview feature allows you to preview how Splunk software will index your data before you commit the data to an index. You can use the Data Preview feature to check the following aspects of data parsing1:
Timestamp recognition: You can verify that Splunk software correctly identifies the timestamps of your events and assigns them to the _time field.
Event breaking: You can verify that Splunk software correctly breaks your data stream into individual events based on the line breaker and should linemerge settings.
Source type assignment: You can verify that Splunk software correctly assigns a source type to your data based on the props.conf file settings. You can also manually override the source type if needed.
Field extraction: You can verify that Splunk software correctly extracts fields from your events based on the transforms.conf file settings. You can also use the Interactive Field Extractor (IFX) to create custom field extractions.
The Data Preview feature is available in Splunk Web under Settings > Data inputs > Data preview. You can access the Data Preview feature when you add a new input or edit an existing input1.
The other options are incorrect because:
A) When extracting fields for ingested data. The Data Preview feature can be used to verify the field extraction for data that has not been ingested yet, but not for data that has already been indexed. To extract fields from ingested data, you can use the IFX or the rex command in the Search app2.
B) When previewing the data before searching. The Data Preview feature does not allow you to search the data, but only to view how it will be indexed. To preview the data before searching, you can use the Search app and specify a time range or a sample ratio.
C) When reviewing data on the source host. The Data Preview feature does not access the data on the source host, but only the data that has been uploaded or monitored by Splunk software. To review data on the source host, you can use the Splunk Universal Forwarder or the Splunk Add-on for Unix and Linux.

The HTTP Event Collector (HEC) supports indexer acknowledgment to confirm event delivery. Each acknowledgment is associated with a uniqueGUID(Globally Unique Identifier).
GUID ensures events are not re-indexed in the case of retries.
Incorrect Options:
B, C, D:These are not valid channel values in HEC acknowledgments.
References:
Splunk Docs: Use indexer acknowledgment with HTTP Event Collector

"When ingesting event data, the measured data volume is based on the new raw data that is placed into the indexing pipeline. Because the data is measured at the indexing pipeline, data that is filetered and dropped prior to indexing does not count against the license volume qota."
https://docs.splunk.com/Documentation/Splunk/8.0.6/Admin/HowSplunklicensingworks

https://docs.splunk.com/Documentation/Splunk/latest/Security/Aboutusersandroles#Role_inheritance
https://docs.splunk.com/Documentation/Splunk/7.3.1/Security
/Aboutusersandroles#How_users_inherit_capabilities

Reference:https://community.splunk.com/t5/Getting-Data-In/Do-we-need-a-license-for-Heavy-forwarder/m-p
/210451