What are two southbound APIs?

OpenFlow and NETCONF are southbound interfaces because they are used between a controller or automation system and network devices. Southbound APIs carry instructions toward the infrastructure: switches, routers, and other forwarding devices. OpenFlow is the classic SDN example because it lets a controller influence forwarding behavior in network devices. NETCONF is also a southbound management protocol; it uses structured XML-based remote procedure calls to retrieve or modify device configuration and operational data. Thrift and CORBA are general distributed-computing technologies, not the CCNA-standard southbound networking answers here, and DSC is not a normal Cisco SDN southbound API in this context. Cisco CCNA v1.1 automation objectives expect the candidate to separate northbound and southbound communication. Northbound APIs face applications and orchestration systems. Southbound APIs face the managed network devices. Because both OpenFlow and NETCONF operate on the controller-to-device side, A and B are the correct selections.