程序设计语言可划分为低级语言和高级语言两大类。与高级语言相比，用低级语言开发的程序，其(27)，但在(28)的场合，还经常全部或部分地使用低级语言。在低级语言中，汇编语言与机器语言十分接近，它使用了(29)来提高程序的可读性。高级语言有许多种类，其中，PROLOG是一种(30)型语言，它具有很强的(31)能力。

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Password　is　a　secret　series　of(69)that　enables　a　user　to　access　a　file,　computer,　or　program.　On　multi-user　systems,　each　user　must　enter　his　or　her　password　before　the　computer　will　respond　to(70).　The　password　helps　ensure　that(71)users　do　not　access　the　computer.　In　addition,　data　files　and　programs　may　require　a　password.

For　many　years,　the　principle　goal　of　computer(73)was　to　write　short　pieces　of　code　that　would　execute　quickly.　The(74)needed　to　be　small,　because　memory　was　expensive,　and　it　needed　to　be　fast,　because　processing　power　was　also　expensive.

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A(71)is　a　data　type　whose　major　attributes　are　determined　by　the　roles　governing　the　insertion　and　deletion　of　its　elements.　The　only　element　that　can　be　deleted　or　removed　is　the　one　that　was　inserted　most(72).　Such　a　structure　is　said　to　have　a　last-in/first-out(LIFO)behavior,　or　protocol.

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