Option B is the correct answer. Azure Data Lake Storage Gen2 supports POSIX-like access control lists (ACLs), which allow you to manage access to individual files and directories within the data lake. This provides a fine-grained access control mechanism that can be tailored to the specific needs of your organization. Option A is incorrect because RBAC at the storage account level does not provide the granularity required for managing access to individual files and directories. Option C is incorrect because while AAD can be used for user authentication, RBAC at the file and directory level is not supported by Azure Data Lake Storage Gen2. Option D is incorrect because implementing a custom access control system can be complex and may not leverage the built-in security features of Azure Data Lake Storage Gen2.