题目
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．（16） ____ 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．（17） ____ For example，the first letters of"My elephant eats too many eels"spell out the hidden message"Meet me．"（18） ____ You might represent each letter with a number，for example．Let's number the letters of the alphabet，in order，from 1to 26．If we substitute a number for each letter，the message"Meet me"would read"13 5 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．（19） ____ For example，"bridge"might stand for"meet"and"out"might stand for"me．"The message"Bridge out"would actually mean"Meet me．"（20） ____ 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．
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．（16） ____ 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．（17） ____ For example，the first letters of"My elephant eats too many eels"spell out the hidden message"Meet me．"
（18） ____ You might represent each letter with a number，for example．Let's number the letters of the alphabet，in order，from 1to 26．If we substitute a number for each letter，the message"Meet me"would read"13 5 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．（19） ____ For example，"bridge"might stand for"meet"and"out"might stand for"me．"The message"Bridge out"would actually mean"Meet me．"（20） ____ 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．
People have used secret codes for thousands of years．（16） ____ 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．（17） ____ For example，the first letters of"My elephant eats too many eels"spell out the hidden message"Meet me．"
（18） ____ You might represent each letter with a number，for example．Let's number the letters of the alphabet，in order，from 1to 26．If we substitute a number for each letter，the message"Meet me"would read"13 5 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．（19） ____ For example，"bridge"might stand for"meet"and"out"might stand for"me．"The message"Bridge out"would actually mean"Meet me．"（20） ____ 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．
题目解答
答案
DEGFA
16．D．考查文章内容理解以及上下文联系．根据后句内容Code breaking never lags（落后） behind code making．可以判断，该空应该和密码的破译有关，故判断D项：只As long as there have been codes，people have tried to break them．要有密码的存在，人们就会试图去破解它们．符合语境逻辑，可以承接上下文．故选D．
17．E．考查文章内容理解以及上下文联系．根据后面举的例子For example，the first letters are"My elephant eats too many eels"spell out the hidden message"Meet me．"是来真名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：You can hide a message by having the first letters of each word spell it out．你可以拼写每个单词的第一个字母来隐藏信息．符合语境逻辑，故选E．
18．G．考查文章内容理解以及上下文联系．根据后面的解释内容You might represent each letter with a number，for example，let's number the letters of the alphabet，in order，from 1 to 26．可以判断，这是介绍密码设置的又一种方法，故判断G选项：Another way to hide a message is to use symbols to stand for specific letters of the alphabet．另外一种隐藏信息的方式是用符号来代表字母表中的特定字母，符合语境．故选G．
19．F．考查文章内容理解以及上下文联系．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：With a code book，you might write down words that would stand for other words．有了密码书，你就可以写下代表其他单词的单词．可以起到承上启下的作用，故选F．
20．A．考查文章内容理解以及上下文联系．根据空后内容的转折However，it is also hard to keep a code book secret for long．So codes must be changed frequently．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：It is very hard to break a code without the code book．没有密码书是很难破解密码的，符合语境．故选A．
16．D．考查文章内容理解以及上下文联系．根据后句内容Code breaking never lags（落后） behind code making．可以判断，该空应该和密码的破译有关，故判断D项：只As long as there have been codes，people have tried to break them．要有密码的存在，人们就会试图去破解它们．符合语境逻辑，可以承接上下文．故选D．
17．E．考查文章内容理解以及上下文联系．根据后面举的例子For example，the first letters are"My elephant eats too many eels"spell out the hidden message"Meet me．"是来真名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：You can hide a message by having the first letters of each word spell it out．你可以拼写每个单词的第一个字母来隐藏信息．符合语境逻辑，故选E．
18．G．考查文章内容理解以及上下文联系．根据后面的解释内容You might represent each letter with a number，for example，let's number the letters of the alphabet，in order，from 1 to 26．可以判断，这是介绍密码设置的又一种方法，故判断G选项：Another way to hide a message is to use symbols to stand for specific letters of the alphabet．另外一种隐藏信息的方式是用符号来代表字母表中的特定字母，符合语境．故选G．
19．F．考查文章内容理解以及上下文联系．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：With a code book，you might write down words that would stand for other words．有了密码书，你就可以写下代表其他单词的单词．可以起到承上启下的作用，故选F．
20．A．考查文章内容理解以及上下文联系．根据空后内容的转折However，it is also hard to keep a code book secret for long．So codes must be changed frequently．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：It is very hard to break a code without the code book．没有密码书是很难破解密码的，符合语境．故选A．
解析
本题为英语阅读填空题，考查学生对文章逻辑关系和上下文衔接的理解。文章围绕密码学的三种主要类型展开，需根据段落内容选择恰当的句子填入空缺处。解题关键在于：
- 明确段落主题：每段分别介绍密码学的不同类型（首字母密码、符号替换密码、代码书密码）；
- 分析句子功能：判断选项是否与前后文形成逻辑衔接（如举例说明、对比关系）；
- 锁定关键词：通过选项中的核心概念（如"code book"、"symbols"）匹配上下文。
第（16）题
后文提示：Code breaking never lags far behind code making（密码破译紧跟密码制作）。
逻辑关系：后句强调破译与制作的同步性，需引出密码破译的历史背景。
选项匹配：D选项"As long as there have been codes, people have tried to break them"（只要有密码，人们就试图破解）自然衔接后文，说明破译行为的普遍性。
第（17）题
后文举例：首字母"My elephant eats too many eels"拼出"Meet me"。
逻辑关系：例子说明通过首字母隐藏信息，需总结方法。
选项匹配：E选项"You can hide a message by having the first letters of each word spell it out"（通过首字母拼出信息）直接对应例子，明确首字母密码的定义。
第（18）题
后文说明：用数字代表字母（如字母顺序编号）。
逻辑关系：需引出符号替换字母的第二种密码类型。
选项匹配：G选项"Another way to hide a message is to use symbols to stand for specific letters"（用符号代表字母）点明符号替换的核心概念，与后文操作方式一致。
第（19）题
后文举例："bridge"代表"meet"，"out"代表"me"。
逻辑关系：需说明代码书的作用。
选项匹配：F选项"With a code book, you might write down words that would stand for other words"（用代码书记录替代词）解释代码书的功能，为例子提供理论基础。
第（20）题
后文转折：However, it is also hard to keep a code book secret for long（代码书难以保密）。
逻辑关系：需先肯定代码书的优势，再引出缺陷。
选项匹配：A选项"It is very hard to break a code without the code book"（无代码书难以破译）形成对比，突出代码书的双刃剑效应。