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