The core processes in a value chain must add value for the external customers, while support processes

The correct answer to this question is this one: "c. are directly involved in service to the external client. "

There exists the same question from other source with the following choices:
a. do not add value for the customer. 

b. include the order fulfillment process. 

c. are directly involved in service to the external client. 

d. are also part of the supply chain.