The correct answer is A. When FortiNAC-F needs near real-time Layer 2 visibility, it relies on link traps, MAC notification traps, RADIUS, or scheduled/manual Layer 2 polling. The study guide explains that MAC notification traps contain the MAC address learned or removed from the switch MAC address table and the associated port, allowing FortiNAC-F to update its database when hosts connect, disconnect, or move. It also states that MAC notification traps are the preferred method for learning and updating Layer 2 information.

If a newly modeled switch does not show hosts as they connect or move between ports, the likely problem is that MAC notification traps are not correctly configured or not reaching FortiNAC-F. Layer 3 polling failure would affect IP-to-MAC correlation, not the ability to learn which switch port a MAC address is connected to. Disabled scheduled polling could delay updates, but it would not be the best explanation when the expected behavior is immediate host detection during connection or movement testing. Contact polling only checks whether the device is reachable; it does not collect host MAC-to-port visibility.