One ofthe main resposibilities of ICMP is to report(1).Although technology has produced increasingly relaible 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 concern of IP. ICMP was designed, in part, to compensate for this shortcoming. Howerver, ICMP does not (3) errors, it simply report them. Error correction is left to the higher-level potocols. Error messages are always sent to the original (4) because the only information available in the datagram about the route is the source and destination IP addresses. ICMP use the source IP address to sent the error massage to the source of the (5).

空白（2）处应选择（）

A.reliable

B.unreliable

C.available

D.unavailable

李某骑自行车经过一路面施工工地时，掉入没有设置明显标志和采取安全措施的坑中，造成骨折。对于李某的损失，应由（）

A.李某自己承担

B.发包人和承包人共同承担

C.发包人承担

D.承包人承担