邮件服务器使用SMTP的主要目的是(52)。

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Currently 94% of Web users use either Internet Explorer or Firefox, but recently some new(71) have been developed that are beginning to attract attention. The browser Opera is becoming very(72) because of its speed, it is currently the world's fastest browser, and because it is much smaller(73) existing browsers (it can almost fit on a single diskette). It can also(74) the last Web page you visited, so the next time you surf, you can start where you left off. And like the big two, you can get it for free; the catch is that you have to watch blinking ads in one comer, or pay ＄40 for the ad-free (75) of Opera.

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TCP/IP协议集由Internet工作委员会发布并已成为(26)标准。与(27)的情况不同，从来不存在正式的TCP/IP层次结构模型，但根据已开发的协议标准，可以根据通信任务将其分成4个比较独立的层次，即网络接9层、网络互联层、(28)、应用层。

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