A). VCN Peering with IAM policies: This offers secure communication within a controlled environment through dedicated peering connections and granular access control with IAM policies.B. FastConnect with private peering and security zones: This method establishes secure, dedicated connections with additional isolation through security zones within FastConnect.C. Service Gateway endpoint with resource-level IAM policies: This utilizes a managed service for secure communication with fine-grained control over access using resource-level IAM policies.D. Internet Gateway with firewall rules and VPN connection: While this method can establish connections, it relies on the public internet, posing inherent security risks. Publicly exposed resources and the potential for vulnerabilities in individual VPN connections make this option less secure compared to controlled and dedicated solutions like VCN peering, FastConnect, and Service Gateway.