There are two routers RTA and RTB from the source device to the destination device, use the Tracert command to test the path. When detecting the first jump RTA, the source device to a large port of the destination device to send a UDP packet with a TTL of 1, when the packet arrives in RTB, TTL becomes 0, so the RTA respond a ICMP_________ message to the source device .

There are two routers RTA and RTB from the source device to the destination device, use the Tracert command to test the path. When detecting the first jump RTA, the source device to a large port of the destination device to send a UDP packet with a TTL of 1, when the packet arrives in RTB, TTL becomes 0, so the RTA respond a ICMP_________ message to the source device .
A . Time Exceeded
B . Echo Request
C . Echo Reply
D . Port Unreachable

Answer: A