One of the main responsibilities of ICMP is to report （1）. Although technology has produced increasingly reliable transmission media, errors still exist and must be handled. IP is an （2）protocol. This means that error checking and error control are not a concem ofIP JCMP wasdesigned, in part, to compensate for this shortcoming. Howerver, ICMP does not （3）errors, itsimply reports them. Error correction is left to the higher-level protocols. Error messages arealways sent to the original（4） because the only information available in the datagram aboutthe route is the source and destination 1P addresses. ICMP uses the source IP address to send theerror massage to the source of the （5）
（2）是（）
A.reliable
B.unreliable
C.available
D.Unavailable