Apex unit test failures can cause a package installation to fail. According to the Salesforce documentation, "If your package contains Apex code, all tests must complete successfully for your package to install." Incorrect license types, package features not compatible, and object limits exceeded are not valid reasons for a package installation failure.

The app builder should know that a field type change is included in the change set and that it can cause a delay in the deployment. A field type change is a change that modifies the data type of an existing field, such as changing a text field to a number field. A field type change can affect many aspects of Salesforce functionality, such as validation rules, formulas, workflows, reports, dashboards, and more. Therefore, deploying a change set that contains a field type change can take longer than usual and require more testing and verification. Option A, C, and D are not changes that can cause a delay in the deployment.

The new object should have a lookup relationship to the Opportunity object. A lookup relationship creates a link between two objects and allows related records to be viewed in a related list. This can be used to track installation information for each opportunity and give sales reps visibility of all the installations associated with their opportunities. Option B, C, and D are not appropriate for this requirement.

Feed Tracking is the Chatter feature that allows field value changes for certain fields to show up on Chatter. Thanks, Publisher Actions, and Topics are other Chatter features, but they do not relate to field value changes.

Create a page layout with the field and use field-level security to hide the field from all other users is how the app builder should meet the requirement of making the comment field on Review private to anyone outside of HR department. Field-level security can control which profiles can view or edit a field on a record. Create an Apex sharing rule, create a sharing rule to share the field with VP of HR with Role and Subordinates, and create a page layout with the field for HR users and another page layout without the field for all other users are not valid or feasible solutions for this requirement.