Which of the following steps is necessary to create a 1-to-many relationship between a Master Entity A and a Detail Entity B?

To create a 1-to-many relationship between a Master Entity A and a Detail Entity B, it is essential that Entity B includes a reference attribute that points to the identifier of Entity A. This establishes a relational link where each record in Entity A (the "master") can be associated with multiple records in Entity B (the "detail").

By defining this reference in Entity B, you effectively allow each detail record to specify which master record it is related to. This setup enables operations like retrieving all detail records for a specific master record, maintaining data integrity, and implementing cascading behaviors in your application.

The other options do not align with the proper establishment of a 1-to-many relationship. For example, while setting up a new entity or adding reference attributes in different configurations might help organize data, they do not directly support the necessity of the relationship being outlined where Entity B has direct access to Entity A's identifier. Thus, the choice of having a reference attribute in Entity B to Entity A's identifier is the correct approach to achieve the desired relationship.