Which topology is not supported when using vPC?

A.
a single-homed server to a single FEX that is connected to two Cisco Nexus 5500 Series Switches

B.
a dual-homed server to two FEXs, each connected to two Cisco Nexus 5500 Series Switches

C.
a dual-homed server to two FEXs that are connected to one Cisco Nexus 5500 Series Switch

D.
a dual-homed server to a single FEX that is connected to two Cisco Nexus 5500 Series Switches

Explanation:
The figure shows unsupported topology where a vPC is between hosts and two FEXs that are
connected to one Cisco Nexus 5500 Series device. This topology does not provide a good high
availability solution because the server loses the connectivity to the network when the Cisco Nexus
5000 Series device fails.
Figure: Unsupported Topology—Host vPC With One Cisco Nexus 5000 Series Device

If you need to connect a multi-homing server to a pair of FEXs when there is only one Cisco Nexus
5000 Series device, you have the option to run active or standby NIC teaming from the server.

http://www.cisco.com/en/US/docs/switches/datacenter/nexus5000/sw/mkt_ops_guides/513_n1_1
/n5k_enhanced_vpc.html