The Contributor role in Azure does not have the permission to assign roles to other users or manage access control. The Contributor role can perform actions such as creating, modifying, and deleting resources within the scope of a resource group or subscription, but it cannot manage access control. To grant the ability to assign roles and manage access control for Azure resources, you would typically need to assign the User Access Administrator or Owner roles to a user or group. These roles have the necessary permissions to manage access control, including the assignment of roles to other users. Therefore, the correct option is B: Assign User1 the Owner role for VNet1.