再问大全-15-13.，看了讨论也不明白呀~~

大全-15-13.     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?

(A) If a biometric access-control system were made to work by identity, it would not produce any correct admittance decisions.

(B) If a biometric access-control system reliably 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.

(D) Nonbiometric access-control systems—based, for example, on numerical codes—are less likely than biometric ones to admit impostors.（B）

(E) Anyone choosing an access-control system should base the choice solely on the ratio of false refusals to false admittances.

再问一次，看了讨论贴还是不明白，为什么B中说it will sometimes turn away legitimate access-seekers呢？legitimate access-seekers的准入机率不也会提高吗？因为条件放宽了。还是因为impostors的准入挤兑了legitimate access-seekers的机会？（因为存储在系统中的身份是有限的，一人对应一个print...我好象想远了，不过不这么想偶没法理解B...）

麻烦哪位XDJM给讲讲？