Which two places can an app builder go to see a list of available Custom...

 An app builder can go to two places to see a list of available custom Lightning components in their org:

Lightning App Builder: This is a tool that allows an app builder to create and customize Lightning pages using drag-and-drop components. The app builder can see the list of custom Lightning components in the Custom section of the Lightning Components pane1.

Lightning Components in Setup: This is a setup menu that allows an app builder to view, create, edit, and delete custom Lightning components in their org. The app builder can see the list of custom Lightning components in the Lightning Components section of the Setup menu2. Option A and B are not places where an app builder can see a list of custom Lightning components.