第12题: [单项选择]在下面密码分析中，难度最大的是______。 A. 唯密文攻击 B. 已知明文攻击 C. 选择明文攻击 D. 三者难度相当 参考答案:A 答案解析:[知识点] 密码分析学 [评析] 所谓唯密文攻击指密码分析者只知道密文，其他什么都不知道，这种分析难度最大。已知明文攻击，指密码分析者不但知道密文，而且知道明文，利用知道的明文及密文推导出加
第24题: [填空题]People resumed their interest in natural gas as a fuel as a result of __________ of the late 1960s and early 1970s. 参考答案:the oil shortages 答案解析:本题涉及人们重新关注天然气燃料的原因。小标题From Field to Ford 下第二段最后一句为答案出处。题干对原文的句式进行了转换，resumed their interest对应文中的 bro
第25题: [单项选择]The fourth paragraph is mainly about ______. A. how to get food and drinks in the camping area B. what kind of cooking equipment should a camper take C. what kind of food a camper should bring D. what kind of campground a camper should select when cooking and drinking 参考答案:B 答案解析:[分析] 综合题。第四段第一句话即为该段中心：Equipment for cooking varies according to the site the camper chooses．答案应该选B。
