类的实例化过程是一种实例的合成过程，而不仅仅是根据单个类型进行的空间分配、初始化和绑定。指导编译程序进行这种合成的是(47)。重置的基本思想是通过(48)机制的支持，使得子类在继承父类界面定义的前提下，用适用于自己要求的实现去置换父类中的相应实现。

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A Web browser is simply a terminal emulator, designed to display text on a screen. The two essential differences between an ordinary terminal emulator and a Web browser are that the browser knows how to deal with(71), and that it has a mechanism for(72)graphical files. Display text, display graphics, and(73)hyperlinks-there's 99 percent of the(74)value. That's not to say that the manufacturers didn't go all-out to attach a hyperactive efflorescence of useless capabilities onto their browsers. Remember when media channels in the browser were a big deal, instead of the clutter you can't wait to delete from your favorites of bookmarks menu? Remember when client-side Java applets were supposed to become the preferred(75)for application development? Remember frames and all their nasty side effects?

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假设某程序语言的文法如下：

 S→a|b|(T)

 T→TdS|S

 其中，V_T={a，b，d，(，))；V_N={S，T}，S是开始符号。考察该文法，句型(Sd(T)db)是S的一个(28)。

 其中(29)是最左素短语，(30)是该句型的直接短语。

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