Which solution will meet these requirements?

Amazon Aurora PostgreSQL with Babelfish allows SQL Server applications to run directly on Aurora PostgreSQL with minimal code changes. Babelfish adds a SQL Server-compatible endpoint, significantly lowering costs compared to running licensed SQL Server instances on RDS or EC2.

AWS Documentation Extract:

“Babelfish for Aurora PostgreSQL enables Aurora to understand T-SQL and SQL Server wire protocol, allowing you to run SQL Server applications on Amazon Aurora PostgreSQL with lower costs.”

(Source: Babelfish for Aurora PostgreSQL documentation)

A, D: SQL Server on EC2 or RDS incurs high Microsoft licensing costs.

C: Plain PostgreSQL would require more code refactoring than Babelfish.