Most computer systems are (165) to two different groups of attacks: Insider attacks and outsider attacks. A system that is known to be (166) to an outsider attack by preventing (167) from outside can still be vulnerable to the insider attacks accomplished by abusive usage of (168) 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 (169) by tools referred to as Intrusion Detection Systems.

（165）处是（）

A.vulnerable

B.week

C.sensitively

D.helpless

两个杯中分别装有浓度40%与10%的食盐水，倒在一起后混合食盐水浓度为30%。若再加入300克20%的食盐水，则浓度变为25%。那么原有40%的食盐水（）克。

A．200

B．150

C．100

D．50