Final answer:
The msdb database in Microsoft SQL Server uses the Full Recovery Model by default, which is essential for scheduling and the point-in-time recovery, requiring regular transaction log backups to manage size.
Step-by-step explanation:
The question is asking which of the following system databases in Microsoft SQL Server uses the Full Recovery Model by default. The correct answer is D. msdb. The msdb database is used by SQL Server Agent for scheduling alerts and jobs, and by other features such as SQL Server Management Studio. By default, msdb is configured to use the Full Recovery Model to prevent data loss and to support point-in-time recovery. It is important to regularly backup the transaction log to avoid it becoming too large under the Full Recovery Model.