Explanation:

Self-registration introduces unknown users into your system, so security and proper access control are paramount. These three options represent core security and administrative best practices.

Why A is Correct:
You should never use an out-of-the-box standard profile directly. The best practice is to clone a standard site profile (like "Customer Community Login User" or "Customer Community User") and then customize the clone. This allows you to create a tailored set of permissions for your specific site without affecting other sites that might use the standard profile, and it protects you from future Salesforce updates that might change the standard profiles.
Why B is Correct:
This follows the principle of least privilege. When users self-register, they should be granted the most restrictive set of permissions necessary to perform their basic tasks. You can always grant additional access later via permission sets if needed. Starting with a restrictive profile minimizes the risk of a new user accidentally or intentionally accessing sensitive data.
Why C is Correct:
Different sites (e.g., a customer self-service portal vs. a partner portal) serve different business functions and user populations. They require different sets of permissions. Using separate profiles for each site allows for precise control over what objects, fields, and records users in each site can access, improving both security and the user experience.

Why the Other Options are Incorrect:

Why D is Incorrect:
This is the anti-pattern that option A warns against. Assigning a standard, un-cloned profile is risky because any changes you make to it will affect all sites and users using that profile. It also leaves you vulnerable to changes in the standard profile from Salesforce releases.
Why E is Incorrect:
Using the same profile for different types of sites (like a self-service site and a partner portal) is a poor security practice. It almost certainly will result in users having either too much access (a security risk) or too little access (a poor user experience).

Reference:
Salesforce Help: Best Practices for Configuring Self-Registration - This article explicitly recommends cloning the standard profile and starting with a restrictive permission set.

Explanation:

Why it's recommended: Lightning Bolt Solutions are specifically designed to package a complete Experience Cloud site, including its theme, pages, content structure, and custom components, for distribution, sharing, and deployment between unrelated orgs. They can be exported from one org and then installed in the new production org.
The Scenario: Moving a site between two production orgs that are not directly connected (meaning they are not a sandbox/production pair) is the classic use case for Lightning Bolt when you want a portable, reusable solution.

❌ Incorrect Answers and Detailed Reasons

A. Deployment via Metadata API
While the Metadata API (ExperienceBundle and Network types) is the standard method for deploying sites from Sandbox to Production, it is generally more complex and error-prone for deployments between completely unrelated production orgs. It requires managing file extraction, handling dependencies, and potentially making manual adjustments for org-specific settings (like user IDs or domain names) in the XML files.

C. Deployment via Change Set
Change Sets can only be used to deploy metadata between connected orgs (e.g., from a sandbox to its related production environment). Since the two production orgs are not directly connected, this option is technically impossible.

B. Publication via Experience Builder
Publishing a site in Experience Builder simply makes the latest changes live within the current Salesforce org. It is not a mechanism for transferring the site's configuration to an entirely different, separate Salesforce org.

Explanation:

A. The Salesforce Administrator is not assigned a role in Salesforce.
A Salesforce administrator must have a defined role in the role hierarchy to be able to create external users, including partner users. If the admin user's record does not have a role assigned, the option to create a partner user from a contact will be unavailable.

C. The account record associated with the contact record is not enabled as a partner.
Before you can enable a contact as a partner user, the contact's parent account must be enabled as a partner account. The "Enable Partner User" action will not appear on a contact record if its associated account does not have partner status.

Why other options are incorrect

B. The Salesforce Administrator is not a member of the Partner Community:
An administrator does not need to be a member of the partner community to manage external users. Their ability to create external users is tied to their profile, permissions, and role within the internal Salesforce organization.

D. The Salesforce administrator is not marked as a delegated administrator on the partner account:
A delegated administrator on a partner account has the permissions to manage users within that partner account, but this is not a requirement for an internal Salesforce administrator to create the initial partner user. An internal admin's ability to create the user is governed by their own permissions and role, and the partner account's status.

Explanation:

In Salesforce, internal sharing settings (like Public Read Only) apply only to internal users — they do not affect external users such as those accessing via Experience Cloud. For Experience Cloud users to view Contact and Account records, you must configure external sharing rules or use Sharing Sets depending on the license type.

🟩 B. Sharing rules should be configured on each object to give Read Only access to Experience Cloud users
This is the correct approach for Customer Community Plus or Partner Community licenses.
You can create criteria-based or owner-based sharing rules to grant Read Only access to external users.
This ensures that Experience Cloud users can view the necessary Contact and Account records.

❌ Why the Other Options Are Incorrect
A. The external sharing model should be updated so that the Account object is private but the Contact object remains public only
This would restrict access further. Making Account private would block visibility unless additional sharing rules are added.

C. The existing sharing model should be updated so that the Contact and Account Objects are private…
This is unnecessary. You don’t need to make objects private to use sharing rules. Also, this could reduce visibility for internal users.

D. The internal sharing model should be updated so that the Contact and Account objects are Public Read Only
This is already the case — and it doesn’t help external users. Internal sharing settings don’t apply to Experience Cloud users.

Reference:
Salesforce Help – External Sharing Model

Explanation:

Why these are correct
B. “ExperienceBundle enables creating experiences across orgs.”
Interpreting through the typos: ExperienceBundle is a metadata type for Experience Builder sites that you can retrieve, edit, and deploy between orgs via the Metadata API/Salesforce CLI. This is the supported way to move an Experience Cloud site (its pages, theme, nav, branding, etc.) from sandbox to production or across orgs.
D. “ExperienceBundle provides editable community metadata in a human-readable format.”
ExperienceBundle stores the site’s configuration as text/JSON files (not a binary .site file like the old SiteDotCom type). This makes the site metadata human-readable and diff-able, so teams can review changes, version-control them, and even programmatically modify them before deploying.

Why the other options aren’t right

A. “ExperienceBundle allows us to programmatically edit any community but using Experience Builder.”
This is contradictory. You don’t need Experience Builder to “programmatically edit”; the point of ExperienceBundle is that you can edit the JSON files directly and then deploy. Salesforce Developers
C. “ExperimentBundle provides editable community metadata…”
This appears to be a typo/duplicate of D. The valid concept is already captured by D (ExperienceBundle’s human-readable JSON).

References
ExperienceBundle for Experience Builder Sites — overview of the text-based (JSON) metadata for pages, themes, branding, etc.
ExperienceBundle | Metadata API Developer Guide — how to retrieve/deploy ExperienceBundle metadata.
Deploy Your Experience Cloud Site with the Metadata API — moving sites between orgs.
Developer Blog: “Buh-bye SiteDotCom, hello ExperienceBundle” — human-readable, programmatic edits, CLI usage.