Datagram networks and virtual-circuit networks differ in that ( ). A. datagram networks are circuit-switched networks, and virtual-circuit networks are packet-switched networks. B. datagram networks are packet-switched networks, and virtual-circuit networks are circuit-switched networks. C. datagram networks use destination addresses and virtual-circuit networks use VC. numbers to forward packets toward their destination. D. datagram networks use VC. numbers and virtual-circuit networks use destination addresses to forward packets toward their destination.