Which description of the Russian Doll Model is true?

Which description of the Russian Doll Model is true?
A . RDM provides bandwidth sharing while providing bandwidth isolation and protection against QoS degradation, and also provides service differentiation for high-priority, normal-priority and best-effort priority services
B . RDM matches simple bandwidth control policies setting individual bandwidth constraint for a given class type and simultaneously limit the aggregate of reserved bandwidth across all class types
C . RDM can be used simultaneously to ensure bandwidth efficiency and to protect against QoS degradation of all class types, whether preemption is used or not
D . RDM guarantees a predefined amount of bandwidth for each type and at the same time allows the bandwidth sharing by defining two pools for every class type: private pool (guaranteed bandwidth) and common pool (bandwidth shared between all class types)

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Answer: C