Apple Business Manager (ABM) supports the distribution of multiple app types via Managed Distribution: custom apps (developed in-house), free apps (from the App Store), and purchased apps (bought through ABM's Apps and Books section). This flexibility allows organizations to manage all app needs within ABM, assigning them to users or devices via MDM. Options A, B, and C are all correct individually, but D encompasses them all, aligning with ABM's comprehensive capabilities as outlined in the Apple Business Manager User Guide.