The question asks about controlling which ports on Azure virtual machines are accessible from the Internet. A network security group (NSG) is specifically designed for this purpose, as it contains security rules that allow or deny network traffic based on source/destination IP addresses, ports, and protocols. The community discussion strongly supports this, with 100% of answers selecting A, high upvotes on comments explaining NSG functionality, and references to Microsoft documentation confirming NSGs filter traffic to Azure resources. Other options are unsuitable: Azure AD roles and groups manage user access and permissions, not network traffic, while Azure Key Vault secures secrets, keys, and certificates, not port access.