The foundational Exadata configuration is constructed from two distinct server tiers: database servers that execute Oracle Database workloads and Exadata Storage Servers that provide intelligent, scale-out database storage. Oracle's Exadata technical architecture identifies the base configuration as two database servers and three storage servers .

Two database servers provide the minimum database compute topology necessary for the architecture's availability and clustered database capabilities. A single database server would eliminate the server-level redundancy expected from the standard Exadata infrastructure design. On the storage side, three Exadata Storage Servers form the baseline storage configuration and support the redundancy mechanisms used by Oracle Automatic Storage Management and Exadata storage services.

Oracle documents the same two-database-server/three-storage-server starting configuration across current Exadata architectural material. Additional database or storage servers can be added in supported elastic configurations, but those expansions do not alter the minimum starting configuration asked for in the question.

Therefore, B and D are correct. Two storage servers are below the supported storage-server baseline, while one database server does not constitute the standard Exadata base infrastructure.

Study Guide reference: Provision and operate Oracle AI Database@Azure Resources — Exadata Infrastructure architecture, database servers, storage servers, infrastructure sizing.

===============