Explanation
https://docs.splunk.com/Documentation/Splunk/8.0.2/Knowledge/SetupaGETworkflowaction Define a GET workflow action Steps Navigate to Settings > Fields > Workflow Actions.
Click New to open up a new workflow action form.
Define a Label for the action.
The Label field enables you to define the text that is displayed in either the field or event workflow menu.
Labels can be static or include the value of relevant fields.
Determine whether the workflow action applies to specific fields or event types in your data.
Use Apply only to the following fields to identify one or more fields. When you identify fields, the workflow action only appears for events that have those fields, either in their event menu or field menus. If you leave it blank or enter an asterisk the action appears in menus for all fields.
Use Apply only to the following event types to identify one or more event types. If you identify an event type, the workflow action only appears in the event menus for events that belong to the event type.
For Show action in determine whether you want the action to appear in the Event menu, the Fields menus, or Both.
Set Action type to link.
In URI provide a URI for the location of the external resource that you want to send your field values to.
Similar to the Label setting, when you declare the value of a field, you use the name of the field enclosed by dollar signs.
Variables passed in GET actions via URIs are automatically URL encoded during transmission. This means you can include values that have spaces between words or punctuation characters.
Under Open link in, determine whether the workflow action displays in the current window or if it opens the link in a new window.
Set the Link method to get.
Click Save to save your workflow action definition.

Reference:
The search command is used to filter or refine your search results based on a search string that matches the events2. The search command behaves exactly like search strings before the first pipe, which means that you can use the same syntax and operators as you would use in the initial part of your search2. Therefore, option D is correct, while options A, B and C are incorrect because they are not true statements about the search command.

Splunk alerts can be based on searches that run in real-time or on a regular schedule3. An alert is a way to monitor your data and get notified when certain conditions are met3. You can create an alert by specifying a search and a triggering condition3. You can also specify how often you want to run the search and how you want to receive the alert notifications3. You can run the alert search in real-time, which means that it continuously monitors your data as it streams into Splunk3. Alternatively, you can run the alert search on a regular schedule, which means that it runs at fixed intervals such as every hour or every day3. Therefore, options A and B are correct, while option C is incorrect because it is not a way to run an alert search.

Reference:
https://docs.splunk.com/Documentation/Splunk/8.0.3/Knowledge/Definesearchmacros