1. suppose a process in host c has a udp socket with port number 6789. sup- pose both host a and host b each send a udp segment to host c with destination port number 6789. will both of these segments be directed to the same socket at host c? if so, how will the process at host c know that these two segments originated from two different hosts?

Yes. Host A and B have the same destination port numbers and thus, their UDP segments will arrive to the socket at host C. In this case, the UDP sockets are represented by the protocol IP and Port. Host C will be able to differentiate between them by doing a check on the source IP and source port from the UDP header.

i believe the answer would be b. within an intersection or on a crosswalk. hope this ! : )