The correct answer is B. Reusable pieces of search processing language.
The explanation is as follows:
Search macros are knowledge objects that allow you to insert chunks of SPL into other searches12.
Search macros can be any part of a search, such as an eval statement or a search term, and do not need to be a complete command12.
You can also specify whether the macro field takes any arguments and define validation expressions for them12.
Search macros can help you make your SPL searches shorter and easier to understand3.
To use a search macro in a search string, you need to put a backtick character () before and after the macro name[^1^][1]. For example, mymacro`.

The fields sidebar is a panel that shows the fields that are present in your search results2. The fields sidebar does not show all extracted fields, which are fields that are extracted from your raw data using various methods such as regular expressions, delimiters or key-value pairs2. The fields sidebar only shows selected fields and interesting fields2. Selected fields are fields that you choose to display in your search results by clicking on them in the fields sidebar or by using the fields command2. Interesting fields are fields that appear in at least 20 percent of events or have high variability among values2. Therefore, option C is correct, while options A and B are incorrect because they are types of fields that the fields sidebar does show.

Reference:https://docs.splunk.com/Documentation/Splunk/8.0.3/SearchReference/Transaction

In Splunk, data sets used in the Pivot tool are derived from data models. The Pivot tool allows users to create reports and visualizations based on the structured information available in data models.
References:
* Splunk Docs - Pivot tool

The correct answer is B. Calculated fields can be chained together to create more complex fields.
Calculated fields are fields that are added to events at search time by using eval expressions. They can be used to perform calculations with the values of two or more fields already present in those events. Calculated fields can be defined with Splunk Web or in the props.conf file. They can be used in searches, reports, dashboards, and data models like any other extracted field1.
Calculated fields can also be chained together to create more complex fields. This means that you can use a calculated field as an input for another calculated field. For example, if you have a calculated field named total that sums up the values of two fields named price and tax, you can use the total field to create another calculated field named discount that applies a percentage discount to the total field. To do this, you need to define the discount field with an eval expression that references the total field, such as:
discount = total * 0.9
This will create a new field named discount that is equal to 90% of the total field value for each event2.
References:
* About calculated fields
* Chaining calculated fields