What is used to combine HP Integrity BL860c server blades into HP Integrity BL870c or BL890c server

What is used to combine HP Integrity BL860c server blades into HP Integrity BL870c or BL890c
server blades?

A.
Virtual Connect

B.
Blade Link

C.
Crossbar Fabric

D.
I/O Expansion Enclosures (IOX)