Explanation
The correct answer is B. Delimiters. This is because the delimiters method is designed for structured event data, such as data from files with headers, where all of the fields in the events are separated by a common delimiter, such as a comma or space. You can select a sample event, identify the delimiter, and then rename the fields that the field extractor finds. You can learn more about the delimiters method from the Splunk documentation1. The other options are incorrect because they are not suitable for comma-separated data. The regular expression method works best with unstructured event data, where you select and highlight one or more fields to extract from a sample event, and the field extractor generates a regular expression that matches similar events and extracts the fields from them. The eval expression is a command that lets you calculate new fields or modify existing fields using arithmetic, string, and logical operations. The table extraction is a feature that lets you extract tabular data from PDF files or web pages. You can learn more about these methods from the Splunk documentation23 .

During the validation step of the Field Extractor workflow, you can remove values that aren't a match for the
field you want to define2. The validation step allows you to review and edit the values that have been
extracted by the FX and make sure they are correct and consistent2. You can remove values that aren't a
match by clicking on them and selecting Remove Value from the menu2. This will exclude them from your
field extraction and update the regular expression accordingly2. Therefore, option A is correct, while options
B and C are incorrect because they are not actions that you can perform during the validation step of the Field
Extractor workflow.

The search modes determine how Splunk processes your search and displays your results2. There are three search modes: Fast, Smart and Verbose2. The search mode that automatically returns all extracted fields in the fields sidebar is Verbose2. The Verbose mode shows all the fields that are extracted from your events, including default fields, indexed fields and search-time extracted fields2. The fields sidebar is a panel that shows the fields that are present in your search results2. Therefore, option C is correct, while options A and B are incorrect because they are not search modes that automatically return all extracted fields in the fields sidebar.

https://docs.splunk.com/Documentation/Splunk/8.0.2/SearchReference/Eval
The eval command calculates an expression and puts the resulting value into a search results field.
If the field name that you specify does not match a field in the output, a new field is added to the search
results.
If the field name that you specify matches a field name that already exists in the search results, the
results of the eval expression overwrite the values in that field.