下列说法中正确的是（　　）

A．可逆反应的特征是正反应速率和逆反应速率相等

B．在其他条件不变时，升高温度可以使化学平衡向放热反应的方向移动

C．在其他条件不变时，增大压强会破坏有气体存在的反应的平衡状态

D．在其他条件不变时，使用催化剂可以改变化学反应速率，但不能改变化学平衡状态

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