The correct answer is A. Highlights panel.

In Lightning Experience, record actions such as New Task appear in the Highlights Panel area of the Lightning record page. Salesforce documentation explains that the actions in the highlights panel come from the object’s page layout, specifically the Salesforce Mobile and Lightning Experience Actions section, unless dynamic actions are enabled.

Since the custom action was already added to the Mobile & Lightning Actions section on the page layouts, the app builder must add the Highlights Panel component to display those actions on the Lightning record page.

Activities shows activity timeline/composer-related functionality, but it is not where page-layout actions are generally displayed. Related Lists and Related Record do not display the main action bar.

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