The correct answer is C because storing large binary objects such as documents directly in a relational database increases database size, raises storage cost, and can degrade performance over time. Amazon S3 is a more appropriate service for storing large unstructured objects like documents, images, and media files. The application can store the actual document files in S3 and keep only the related metadata, object keys, and references in the existing Oracle database.

This design is more cost-effective because S3 storage is generally less expensive than expanding high-performance relational database storage for BLOB content. It also improves database performance because the database no longer needs to manage the overhead of storing and retrieving large document payloads. The database can focus on transactional and relational data, which is the workload it is designed to handle best.

S3 also provides high durability, scalability, and resilience. These characteristics satisfy the requirement for a highly available and resilient solution while avoiding unnecessary expansion of the RDS storage layer. Keeping metadata in the existing database minimizes the application changes compared with a full database migration.

Option A is incorrect because Magnetic storage would significantly reduce performance and is not appropriate for this workload. Option B would improve performance, but it would be much more expensive and does not address the root cause of storing large BLOBs in a relational database. Option D is incorrect because moving the relational Oracle workload to DynamoDB would require a major redesign and is not the most cost-effective solution for the stated problem.

The best architectural pattern is to use Amazon S3 for document storage and the relational database for metadata and transactional records.