题目内容
【题目】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. 【1】 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. 【2】 For example, the first letters of “My elephant eats too many eels” spell out the hidden message “Meet me.”
【3】 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 “135 520 135.”
A code uses symbols to replace words, phrases, or sentences. To read the message of a real code, you must have a code book. 【4】 For example, “bridge” might stand for “meet” and “out” might stand for “me.” The message “Bridge out” would actually mean “Meet me.” 【5】 However, it is also hard to keep a code book secret for long. So codes must be changed frequently.
A. It is very hard to break a code without the code book.
B. In any language, some letters are used more than others.
C. Only people who know the keyword can read the message.
D. As long as there have been codes, people have tried to break them.
E. You can hide a message by having the first letters of each word spell it out.
F. With a code book, you might write down words that would stand for other words.
G. Another way to hide a message is to use symbols to stand for specific letters of the alphabet.
【答案】
【1】D
【2】E
【3】G
【4】F
【5】A
【解析】
试题分析：本文是一篇说明文，主要介绍了密码的设置方法和破解的方法。
【1】D根据后句内容可以判断该空应该和密码的破译有关，故判断D项内容符合语境逻辑，可以承接上下文。
【2】E后面举的例子是来证明人们设置密码时往往会利用一些单词的第一个字母来作为密码，由此判断E选项内容符合语境逻辑。
【3】G根据后面的解释内容可以判断这是介绍密码设置的又一种方法，故判断G选项符合语境。
【4】F根据后面的举例以及前句中的 a code book可以判断该句是介绍密码书的使用，故判断F选项可以起到承上启下的作用。
【5】A根据空后内容的转折可知尽管利用密码书可以破译密码，但是一本密码书也不会使用很久的时间，故判断A选项符合语境。
