Which item is required for communication between Cisco Unified Computing System Manager and VMware vCenter?

Answer is C

Connecting Cisco UCS Manager to VMware vCenter

Step 1 In the Navigation pane, click the VM tab.
Step 2 On the VM tab, expand the All node.
Step 3 On the VM tab, click VMWare.
Step 4 In the Work pane, click the General tab.
Step 5 In the Actions area, click Modify Extension Key.
Step 6 In the Modify Extension Key dialog box, do the following:
a) In the Key field, modify the key as needed.
A vCenter extension key can have a maximum length of 33 characters. These characters can be letters,
numbers, or hyphens. No other characters or spaces are permitted in the extension key.
b) Click OK.

http://www.cisco.com/c/en/us/td/docs/unified_computing/ucs/sw/vm_fex/vmware/gui/config_guide/b_GUI_VMware_VM-FEX_UCSM_Configuration_Guide/b_GUI_VMware_VM-FEX_UCSM_Configuration_Guide_chapter_0101.pdf