What administrative feature lets org admins control which apps can be installed workspace-wide?

Slack's app approval and app-management controls allow administrators to govern application installation and usage. Workspace Owners can enable app approval, pre-approve applications, restrict applications, and determine whether members can request unapproved apps. In Enterprise organizations, Org Owners can establish organization-level app-management policies that enable app approval across workspaces and control which applications may be installed or used. Enterprise administrative interfaces also support approving, restricting, installing, and distributing apps across selected workspaces. Block Kit Builder is a UI-design utility, Socket Mode is an event-delivery mechanism, and the Events API delivers Slack activity notifications; none of those features governs app installation policy. Therefore, option A is the correct administrative control for determining which applications users are allowed to install or request within managed Slack environments.