The correct answer is C. Dynamic action.
Dynamic Actions allow an app builder to control which actions appear on a Lightning record page and apply filters to control action visibility. Salesforce documentation states that Dynamic Actions can be assigned in Lightning App Builder and visibility filters can control when actions are shown.
For this requirement, the custom Sync action can be shown only when the Account custom Status field equals Ready to Sync. A custom link alone does not provide the same Lightning App Builder visibility control, a formula field cannot call the Lightning Web Component action, and an AppExchange product is unnecessary.

The correct answer is D. Component visibility filter.
In Lightning App Builder, component visibility rules can control whether a component appears based on context, including the device/form factor. Salesforce Trailhead specifically describes creating a visibility rule so a component appears only when the page is viewed on a phone, which matches restricting a Lightning component to mobile users.
A is incorrect because form factor settings are generally used for page/device availability or preview behavior, not the best feature for hiding or showing one specific component on a single Lightning record page.
B and C are incorrect because the Highlights Panel and Related List Quick Links are page components, not conditional visibility tools.

Feed Tracking is the correct feature because Salesforce can automatically generate feed updates when a tracked field changes on a record. Salesforce Help explains that feed tracking detects changes to tracked record fields and posts updates to the feed. It can also be configured for custom objects.
For this scenario, the app builder would track the travel request approval/status field. When the request becomes Approved, Salesforce posts that tracked change automatically on the record feed.
Why others are incorrect:
Auto-response rule sends automatic email responses, mainly for Lead/Case scenarios.
Approval process manages record approval routing, but the feature that creates automatic feed posts for field changes is Feed Tracking.
Feed quick action is manual, not automatic.

Use a Component visibility filter. The issue is not object access or field access. The Contact Lightning record page is shared, but one component should be hidden for users with the Marketing profile. Salesforce Lightning App Builder supports visibility filters on Lightning page components, so the app builder can conditionally show or hide that component based on user/profile criteria.
Why not the others? AppExchange is unrelated. Detail page layouts control field layout, not visibility of a Lightning page component. Field-level security controls field access, not whether a large component appears on a Lightning record page.

The correct answer is D. Set the Organization-Wide Default to Private for accounts. Create criteria-based sharing rules for each marketing team, and create an Inside Sales Team profile with the "View All" setting for Accounts.
The field sales team should only see Accounts they own, so Account OWD must be Private. Salesforce OWDs define users' default access to records they do not own.
North American and European marketing teams need access by region, so use criteria-based sharing rules based on the Account region. Salesforce criteria-based sharing rules share records when records match field criteria.
Inside sales needs access to all Account records, so give that group View All Records on Account. Salesforce object permissions define that View All Records lets users view all records for that object regardless of sharing settings.