P213 159

antonia

P213 159
  Biometric access-control systems---those using fingerprints, voiceprints, etc., to regulate admittance to restricted areas—work by degrees of similarity, not by identity. After all, even the same finger will rarely leave exactly identical prints. Such systems can be adjusted to minimize refusals of access to legitimate access-seekers. Such adjustments, however, increase the likelihood of admitting impostors.
---Which of the following conclusions is most strongly supported by the information above?
(B) If a biometric access-control system reliable prevents impostors from being admitted, it will sometimes turn away legitimate access-seekers.
(C) Biometric access-control systems are appropriate only in situations in which admittance of impostors is less of a problem than is mistaken refusal of access.
能帮我分析一下这道题吗？conclusion 和evidence各是什么？我选了C，C是不是错在only上？那请问B为何正确？我觉得原文只交代了一种相反的情况的可能性，不能由此推出B的 情况。

linsonstudy

B实际上是把原题的意思用另一种形式讲了一遍，起加强作用。
原题主要是要强调一个矛盾：引入这个系统后，如果加强此系统的辨认精度，那么就会拒绝部分合法进入者（因为同一个手指头，每次所取的指纹都不是完完全全相同的）；如果降低其辨认精度，就会增加冒名顶替者的进入机会。
C如果理解了意思就知道它和原题是矛盾的，并不是加强。
C的意思是 只当“冒名顶替者进入的机会”少于“错误拒绝合法进入者的机会”的情况下，B system才会运作得合适。