The requirement "The planned service payloads will require minimum transformation. Routing is simple" leads me to believe A. BPEL Process not required since BPEL Process sacrifices performance for better transformation & service orchestration.
https://docs.oracle.com/middleware/1213/osb/develop/GUID-C7FA8DAD-E235-437F-87D8-3FE28BE98A6D.htm#OSBDV2101 says "Service Bus proxy services, along with business services, provide the means for managing services, transforming messages, and routing messages through the enterprise."=>B. Proxy Service
https://docs.oracle.com/cd/E28280_01/admin.1111/e15867/business_services.htm#OSBAG990 says "Business services are Oracle Service Bus definitions of the enterprise services with which you want to exchange messages"=>D. Business Service