One ofthe main resposibilities ofICMP is to report  （） . Although technology hasproduced increasingly relaible transmission media, errors still exist and must be handled. IP isan  （）  protocol. This means that error checking and error control are not a concem ofIP. ICMP was designed, in part, to compensate for this shortcoming. Howerver, ICMP doesnot  （） errors, it simply report them. Error correction is left to the higher-levelpotocols. Error messages are always sent to the original  （）  because the only informationavailable in the datagram about the route is the source and destination IP addresses. ICMP usethe source IP address to sent the error massage to the source ofthe（）.

Error messages are always sent to the original（）because the only informationavailable in the datagram about the route is the source and destination IP addresses.

A．user

B．destination

C．source

D．program

在我国（）一带，有结婚挂门帘的习俗。

A.辽宁铁岭

B.河南信阳

C.河北承德

D.吉林长春