Final answer:
Stand-alone annotation is the correct choice for creating editable text to be added as a layer to many different ArcGIS map documents because it can be customized, remains constant across maps, and is stored in a geodatabase. (option D is the correct answer).
Step-by-step explanation:
If an ArcGIS user wants to create editable text that can be added as a layer to many different map documents, they should create stand-alone annotation. Stand-alone annotation is stored in a geodatabase as an annotation feature class and can be added to multiple map documents. Unlike dynamic labels that change based on scale and attribute values, stand-alone annotation allows for the customization and placement of text, which remains constant across different map documents.
Feature-linked annotation is similar but is directly linked to the features in a feature class, so any changes to the feature attributes would update the annotation. Map annotation, on the other hand, is stored with a specific map document and isn't designed to be shared across multiple documents.