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）
（1）是（）
A.numbers
B.functions
C.strings
D.Errors
参考答案：D
解析：
ICMP的其中一项职责是报告错误，虽然技术导致了日益可靠的传输介质，但是错误依然存在并需要小心处理。IP协议是一个不可靠的协议。这意味着错误检查和错误控制不是IP协议的关注焦点。ICMP的设计是为了部分地弥补这一不足。然而，ICMP不纠正错误，仅仅报告错误。纠错通常是留给更高层的协议。错误消息总是发送到原始的来源，因为数据报中关于路由唯一可用的信息是源IP地址和目的IP地址。ICMP使用源IP地址来发送错误信息到数据报的源地址。