B is correct

B
https://www.learnexperiencecloud.com/article/5-Ways-to-Create-Users-in-Experience-Cloud

There are 5 basic options for how to continue to add users on an ongoing basis:
1. Manually create users. Are you on the phone with a customer and want to grant them access to the site right away? Enable your users to manually create users directly from their contact record.
2. Automatically create a user based off of a business process. This works well if you want to automatically give someone access to your site based upon them signing a contract or completing an onboarding process, for example. This is a good path to take when you know who the users are that you want to grant access to the site.
3. Allow users to self register. This works well when you don’t know who all of your end users are, so cannot give all of them access automatically. This is used extensively in B2B2C use cases, but also in B2B and B2C. The only time you don’t want to setup this option is when you know who all of your users are and plan to grant them all access automatically.
4. Grant existing users the ability to create additional users at their account. This option is good for B2B use cases where you have multiple contacts at a business account who need access to the portal. It is extremely common to see this in partner portals.
5. Create a user when they try to access the site and are already logged into another system that can act as an Identity Provider (IDP). Known as just in time provisioning or registration handling, this option is helpful when you know who your users are (because they’re already logged into one of your systems or another digital property that you own), but you don’t expect all of them to login to your Experience Cloud site and thus don’t want to create all of them as users upfront. In order for this to work, the other system must support acting as an IDP as part of your SSO setup....