To ensure auditing users can access records in the Case_Issue__c junction object, the correct data permissions on related records must be established:
D . Read-Only access on Case and Issue__c. Users need read-only access to both Case and Issue__c objects to view associated Case_Issue__c junction object records properly. This is because access to junction object records in Salesforce is determined by the user's access levels to the parent records in a relationship.
Steps to configure access:
Navigate to Setup → Profiles or Permission Sets.
Select the profile or permission set of the auditing users.
Under Object Settings, adjust the permissions for Case and Issue__c to at least 'Read-Only'.
Ensure that users have visibility to the Case_Issue__c object itself.
This configuration allows users to view the details of cases and issues as they audit the junction object records.

Putting the SC in the role hierarchy above the technicians whose work orders they review will provide the required access, given a private data model. The role hierarchy determines how users can access records they do not own. Users at any given role level can view, edit, and report on all data owned by or shared with users below them in the role hierarchy.

The two features of Chatter that would meet CK's business needs are: Set up new public Chatter groups. A public Chatter group is a way to create a collaborative space for users to share information, files, polls, and ideas around a common topic or interest. A public Chatter group can be joined by any user in the organization and can be seen by anyone who has access to Chatter. By setting up new public Chatter groups, CK can enable users to socialize and collaborate around customer accounts and discuss various topics. Use post action on the Account object. A post action is a type of quick action that allows users to create a post on a record's feed or on their own feed. A post can include text, mentions, hashtags, topics, links, files, or images. By using post action on the Account object, CK can enable users to share updates, feedback, or questions about customer accounts and engage with other users who follow the accounts. Set up new private Chatter groups is not a valid feature, as it does not meet CK's business needs. A private Chatter group is a way to create a collaborative space for users to share information, files, polls, and ideas around a confidential or sensitive topic or interest. A private Chatter group can only be joined by invitation and can only be seen by the group members. By setting up new private Chatter groups, CK would limit the visibility and accessibility of the conversations around customer accounts. Use Chatter actions to create tasks to complete is not a valid feature, as it does not meet CK's business needs. A Chatter action is a type of quick action that allows users to create a task from a record's feed or from their own feed. A task can include subject, due date, priority, status, assigned to, etc. By using Chatter actions to create tasks to complete, CK would enable users to track and manage their work related to customer accounts, but not to socialize and collaborate with other users.

A validation rule is a formula that evaluates the data in one or more fields and returns a value of "True" or "False". Validation rules verify that the data a user enters in a record meets the standards you specify before the user can save the record. In this case, a validation rule can be used to check if the Expected_Close_Date_c field is populated before the Opportunity stage is set to qualified