Service a Is Invoked by Desktop Application A, Which Requests

Multiple Choice

Service A is invoked by Desktop Application A, which requests a data value from Service A. In order for Service A to retrieve this data value, it must invoke Service B, which retrieves the value from Database A. Which participant(s) in this scenario are considered service consumers?    SELECT ALL THAT APPLY

A) Service A
B) Service B
C) Desktop Application A
D) Database A