The correct answers are A. Set up new public Chatter groups and D. Use post action on the Account object.
Public Chatter groups support open collaboration where company users can share information in a group feed.
Salesforce Chatter groups are designed for teams to share information, files, and discussions.
Post action on the Account object allows users to discuss customer accounts directly from the Account record feed. Salesforce Chatter feeds appear on record pages and allow users to follow records and see updates about them.
Why others are incorrect:
Private Chatter groups are not suitable because CK wants all company employees to see the conversations.
Chatter actions to create tasks help assign work, but they do not primarily solve open company-wide collaboration around accounts.

The correct answer is A. Sharing rules.
Because the Account OWD is Private, users can't automatically see records owned by users in another branch of the role hierarchy. Salesforce sharing rules are used to extend record access beyond the organization-wide default and role hierarchy. Salesforce documentation states that sharing rules grant additional access to users in public groups, roles, or territories.
Why others are incorrect:
B). Public groups can be used inside a sharing rule, but the public group alone does not share records.
C). Aliases are user display shortcuts, not security controls.
D). Assignment rules assign records; they do not grant cross-team record visibility.

Users need Read access to both master objects.
Request Inventory is a junction object with two master-detail relationships: Inventory and Order. For junction objects, access is based on the associated master records and the sharing behavior of the master-detail relationships. Salesforce documentation for object relationship considerations explains that sharing access to a junction object record is determined by access to both associated master records.
Why not the others? Sharing rules are not created directly on a master-detail detail object in the same way, because it is controlled by parent. Apex-based sharing is not needed. Read access to only the first master object is not enough because the junction record connects two master records.

The correct answer is D. Approval process.
The marketing director wants all free parts to receive sign-off before they are allowed. Salesforce Approval Processes are used to automate how records are approved, define who approves at each step, and specify actions after approval or rejection. Trailhead describes approval processes as automation for record approval and explains that approval steps assign approval requests to specific users.
Chatter approval is not the standard feature for formal record sign-off. Slack post and automated email message can notify people, but they do not enforce approval. An Approval Process is the correct declarative feature for required business sign-off.

The correct answers are C. Lightning App Builder and D. Lightning components in Setup.
In Lightning App Builder, custom Lightning components that are configured for use in Lightning App Builder appear in the Lightning Components pane.
In Setup # Lightning Components, Salesforce allows admins to view a list of Lightning Web Components and Aura components in the org.
Why others are incorrect:
A). Visualforce components in Setup lists Visualforce custom components, not Lightning components.
B). Salesforce Optimizer App analyzes org configuration and recommendations; it is not the place to list available custom Lightning components.