When deploying from a sandbox on a newer Salesforce version to production on a current version, any components that rely on features not yet available in production will fail.
Change sets do not automatically upgrade production.
All features must be supported in the target org at deployment time.
Salesforce documentation notes that compatibility issues may occur if components use version-specific features, and deployments must be tested against the target org's current version. (Salesforce Help) A is incorrect because deployments do not automatically wait for production upgrades.
B is partially true, but deployments are possible if features are supported.
C is incorrect; components are not automatically upgraded.

The correct answer is C. Add the standard Chatter feed component.
In Lightning App Builder, Salesforce provides a standard Chatter component for record pages. Salesforce documentation states that the Feed component was renamed Chatter in Lightning App Builder and is used to place the publisher and feed on a record page.
A is incorrect because a related list component does not add the Chatter feed.
B is incorrect because the standard Chatter component is available in Lightning App Builder; it does not need to come from AppExchange.
D is incorrect because a custom component is unnecessary when Salesforce provides the standard Chatter component.

The correct answers are A. Review the Contact record and ensure it is linked to an Account, C. Verify the users with the issue have access to the Contact object, and E. Confirm whether Default Organization-Wide Sharing Settings provide access to the Account.
A Contact that is not linked to an Account is treated as a private contact. Salesforce states that contacts without an account are private regardless of the sharing model, so checking whether the Contact is associated with an Account is a valid troubleshooting step.
Users also need object-level access to the Contact object. Object permissions control whether users have base-level access such as read, create, edit, and delete for an object.
Finally, Contact visibility is often affected by Account access, especially when Contact sharing is controlled by the parent Account. Organization-Wide Defaults define the default record access users have for records they do not own, so checking the Account OWD is also correct.
B is incorrect because creating a new Contact does not troubleshoot the actual sharing/security issue.
D is incorrect because creating a broad Account Sharing Rule for all records is not the first troubleshooting step and may overexpose data.

The correct answer is D.
Validation rules are the right declarative tool to enforce data compliance before a record is saved. They can prevent a Case from moving backward to an earlier Status and can require specific fields when Case criteria are met. Salesforce formula functions such as ISCHANGED() compare whether a field value changed, and validation rules can use formula logic to stop invalid saves.
Why others are incorrect:
Approval Process is for routing records for approval.
Dependent picklists control picklist value availability, not status regression.
Case Flow can automate case processes, but validation rules are the best tool for enforcing save-time compliance.

The correct answer is B.
This is a one-user exception. Salesforce recommends using permission sets to extend access without changing the user's base profile. A permission set can grant read-only field access through field-level security to just the selected customer service agent. Salesforce documentation explains that permission sets extend user access, and field permissions control whether users can view or edit individual fields.
Why others are incorrect:
A creates a new profile for one user, which is not the recommended scalable solution.
C is not accurate because field-level security is assigned through profiles or permission sets, not directly to one user from the field alone.
D would give all users with the Customer Service profile read-only access, not only the single agent.