802.11r enhances roaming. TheApple Platform Deployment Guidestates, "802.11r, or Fast BSS Transition, improves Wi-Fi performance by enabling faster roaming between access points, reducing authentication overhead." Option C is a QoS feature, not a standard, and A and D are unrelated.
[References:, Apple Platform Deployment Guide, "Wi-Fi Standards" section., macOS Deployment Reference, "Network Optimization" section., ]
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