第二节 （共 5 小题，每小题 2 分，满分 10 分）
根据短文内容，从短文后的选项中选出能填入空白处的最佳选项，选项中有两项为多余选项。
Secret codes (密码)keep messages private。Banks, companies, and government agencies use secret codes in doing business, especially when information is sent by computer.
People have used secret codes for thousands of years. _ Code breaking never lags(落后) far behind code making. The science of creating and reading coded messages is called cryptography.
There are three main types of cryptography. _ For example, the first letters of “My elephant eats too many eels” Spell out the hidden message “Meet me.”
_ You might represent each letter with a number, For example, Let’s number the letters of the alphabet, in order, from 1 to 26. If we substitute a number for each letter, the message “Meet me” would read “13 5 20 13 5.”
A code uses symbols to replace words, phrases, or sentences. To read the message of a real code, you must have a code book._For example, ”bridge“ might stand for “meet” and “out” might stand for “me.” The message “bridge out” would actually mean “Meet me.” _However, it is also hard to keep a code book secret for long. So codes must be changed frequently.
36.
37.
38.
39.
40.
D
根据上面的解题思路可知，。故选项D正确。
根据后一句“Code breaking never lags(落后) far behind code making.”可知，前一句在说解码的事情，也就是break the code。
没有找到关键词break。
E
根据上面的解题思路可知，是把信息藏于单词的首字母中。故选项E正确。
根据后一句“For example, the first letters of “My elephant eats too many eels” Spell out the hidden message “Meet me.”可知，前一句在探讨把信息藏在每个单词的第一个字母里的事情。
没有找到关键词first letters。
G
根据上面的解题思路可知，另一种藏信息的方法是用字母表中的特殊字母来代替。故选项G正确。
根据上一段的第一句“There are three main types of cryptography.可知，有三种密码使用法，而后只讲了一种，所以此处应是讲另一种。
没有把握前面出现的three main types of cryptogrphy。
F
根据上面的解题思路可知，有了密码本，就可以写下代表其他单词的单词了。故选项F正确。
根据前一句“To read the message of a real code, you must have a code book.”可知，前一句在探讨去阅读一条加密的信息，你必须有一本密码本。
没有把握关键词a code book。
A
根据上面的解题思路可知，没有密码本，就很难破解密码。故选项A正确。
根据后一句“However, it is also hard to keep a code book secret for long.”可知，前一句在探讨密码本的问题。
没有把握关键词hard。