What are functional components?

What are functional components?
A . They are inputs to the IT4IT value streams, and pass through a hierarchy of data objects via state changes across the service backbone
B . They are the primary means for understanding business requirements as they are expressed to the Strategy to Portfolio value stream
C . They represent the output of the Requirement to Deploy value stream
D . They are the smallest standalone technology units that are useful to IT service provider

Answer: D