关于SNMP的说法中，“ ______”是正确的。

A．SNMP协议是依赖于UDP协议数据报服务的应用层协议

B．SNMP协议是依赖于TCP协议数据报服务的应用层协议

C．SNMP协议是依赖于UDP协议数据报服务的传输层协议

D．SNMP协议是依赖于TCP协议数据报服务的传输层协议

Most computer systems are (71) to two different groups of attacks：insider attacks and outsider attacks．A system that is known to be (72) to an outsider attack by preventing (73) from outside can still be vulnerable to the insider attacks accomplished by abusive usage of (74) users．Detecting such abusive usage as well as attacks by outsides not only provides information on damage assessment,but also helps to prevent future attacks．These attacks are usually (75) by tools referred to as Intrusion Detection Systems．

（73）处填（）。

A．visit

B．access

C．I/O

D．read/write