To require administrators to access session hosts using the Azure portal, which service should you include in the solution?

Azure Bastion is the correct choice because it provides secure and seamless RDP/SSH connectivity to your virtual machines directly through the Azure portal over SSL. This eliminates the need for public IP addresses on your session hosts and prevents direct exposure to the internet, enhancing security. Azure Firewall is a network security service that protects your Azure Virtual Network resources but doesn't provide direct portal-based access to VMs. Conditional Access policies enforce access controls based on user, device, and location, but they don't facilitate the connection method itself. Microsoft Defender for Cloud is a security posture management and threat protection service, not an access gateway.