A network is composed of several VRFs. It is required that VRF users VRF_A and VRF_B be able  to route to and from VRF_C， which hosts shared services. However， traffic must not be allowed to flow between VRF_A and VRF_B. How can this be accomplished？（）

• A、route redistribution
• B、import and export using route descriptors
• C、import and export using route targets
• D、Cisco MPLS Traffic Engineering