In Splunk, a variable for a macro is defined by placing the variable name inside dollar signs, like this:
$variable name$. This syntax allows the macro to dynamically replace the variable with the appropriate value when the macro is invoked within a search. Using this method ensures that the search strings can be dynamically adjusted based on the variable's value at runtime.
References:
* Splunk Docs: Use macros
* Splunk Answers: Defining and Using Macros

Explanation
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.

The correct answer is B. A field added by an automatic lookup.
A calculated field is a field that is added to events at search time by using an eval expression. A calculated
field can use the values of two or more fields that are already present in the events to perform calculations.A
calculated field can use any field as a source, as long as the field is extracted before the calculated field is
defined1.
An automatic lookup is a way to enrich events with additional fields from an external source, such as a CSV
file or a database.An automatic lookup can add fields to eventsbased on the values ofexisting fields, such as
host, source, sourcetype, or any other extracted field2.An automatic lookup is performed before the calculated
fields are defined, so the fields added by the lookup can be used as sources for the calculated fields3.
Therefore, a calculated field can use a field added by an automatic lookup as a source.
References:
About calculated fields
About lookups
Search time processing