To ensure that User1 can assign the Reader role for VNet1 to other users, you should:
A. Assign User1 the Network Contributor role for VNet1.
The Network Contributor role grants permissions to manage network resources, including virtual networks (VNet1), but restricts access to only those resources.
By assigning User1 the Network Contributor role for VNet1, you provide them with the necessary permissions to manage role assignments specifically for VNet1, including assigning the Reader role to other users.
This approach adheres to the principle of least privilege by granting only the necessary permissions for managing network resources without providing broader access to other resources in the subscription or resource group.
Option C is incorrect because assigning the Owner role for VNet1 provides excessive permissions, allowing User1 to manage all aspects of the virtual network, which exceeds the requirement to assign the Reader role to other users.