41. What is the function of DI-QKD?
- A. To invent new quantum computers.
- B. To make traditional codes easier to crack.
- C. To solve the safety flaws of present encryption.
- D. To replace the internet with quantum network.
答案：C
答案句：Luckily, to protect information, physicists have developed a theoretically reliable system called device-independent quantum key distribution (DI-QKD), which uses entangled (纠缠的) quantum particles (粒子) to fix weak points in existing methods.
参考译文：幸运的是，为了保护信息，物理学家们开发了一种理论上可靠的系统，称为设备无关量子密钥分发（DI-QKD），它利用纠缠的量子粒子来修复现有方法中的弱点。
定位线索：题干“function of DI-QKD”→答案句“fix weak points in existing methods”；文中“fix weak points”对应选项C“solve the safety flaws”；“existing methods”对应“present encryption”。
解析：题干问DI-QKD的功能，答案句明确指出其作用是“fix weak points in existing methods”，即修复现有方法的弱点，与选项C“solve the safety flaws of present encryption”（解决当前加密的安全缺陷）同义。选项A无中生有，文中未提及发明新量子计算机；选项B与原文相反，DI-QKD是保护而非使传统密码更易破解；选项D范围扩大，文中只说为安全量子互联网铺路，并非取代互联网。
42. How does the author explain the weakness of traditional cryptography?
- A. By making a comparison.
- B. By giving an example.
- C. By listing data.
- D. By analyzing causes.
答案：B
答案句：The challenge lies in making sure the key can’t be decoded when sent. For instance, the keys in one popular encryption scheme are based on the main factors of large numbers, which take enormous effort to crack.
参考译文：挑战在于确保密钥在发送时无法被解码。例如，一种流行的加密方案中的密钥基于大数的主要因子，破解这些因子需要巨大的努力。
定位线索：题干“how does the author explain”→答案句“For instance”；文中“For instance”引出例子，对应选项B“giving an example”；例子前观点句“The challenge lies in making sure the key can’t be decoded when sent”是答案依据。
解析：题干问作者如何解释传统密码学的弱点，答案句中“For instance”明确表明作者通过举例说明，即选项B“By giving an example”。例子本身（基于大数因子的密钥）不是答案依据，例子前的观点句“The challenge lies in making sure the key can’t be decoded when sent”才是关键，正确选项正是对该观点句的回应。选项A无中生有，文中未作比较；选项C错误，文中无数据；选项D错误，文中未分析原因。
43. The underlined word “handshake” in Paragraph 3 refers to ________.
- A. physical greeting between researchers
- B. basic test and identity confirmation
- C. formal delivery of secret information
- D. agreement on future research plans
答案：B
答案句：If the sender and receiver entangle (纠缠) a pair of particles across the network, they can each perform tests that confirm the particles’ properties are strongly linked, well beyond chance. After this “handshake”, they can be sure they’re the only ones on the channel.
参考译文：如果发送方和接收方在网络中纠缠一对粒子，他们可以各自执行测试，确认粒子的属性紧密相连，远超偶然。在这次“握手”之后，他们可以确信自己是通道上唯一的人。
定位线索：题干“handshake”→答案句“After this 'handshake', they can be sure they're the only ones on the channel”；文中“perform tests that confirm”和“be sure they're the only ones”对应选项B“basic test and identity confirmation”。
解析：题干问“handshake”的含义，答案句前文描述发送方和接收方执行测试确认粒子属性，后文说“they can be sure they're the only ones on the channel”，表明“handshake”指测试和身份确认过程，即选项B。选项A偷换概念，文中无物理问候；选项C无中生有，握手后才有密钥共享；选项D答非所问，文中未提研究计划。
44. What progress has the Chinese team made in DI-QKD?
- A. They realized long distance link in real city environment.
- B. They invented the theory of quantum entanglement.
- C. They built a complete secure quantum internet.
- D. They succeeded in sending keys over 100 kilometers.
答案：A
答案句：Now, a team in China has demonstrated the technique in real city conditions, an advance that could clear the way for a secure quantum internet in which trust is taken for granted. … Now, the Chinese team led by Jianwei Pan have extended this to practically useful distances. After collecting data for 26 days, they showed they had the statistics to establish and share a key across 11 kilometers.
参考译文：现在，中国的一个团队在真实城市条件下展示了这项技术，这一进步可能为安全的量子互联网铺平道路，其中信任被视为理所当然。……现在，潘建伟领导的中国团队已将其扩展到实际有用的距离。在收集了26天的数据后，他们表明有统计数据可以在11公里范围内建立和共享密钥。
定位线索：题干“progress made by Chinese team”→答案句“demonstrated the technique in real city conditions”和“extended this to practically useful distances”；文中“real city conditions”对应选项A“real city environment”；“11 kilometers”对应“long distance”。
解析：题干问中国团队取得的进展，答案句明确指出他们在“real city conditions”（真实城市条件）下演示了技术，并扩展到“practically useful distances”（实际有用距离），即11公里，与选项A“realized long distance link in real city environment”完全对应。选项B无中生有，纠缠理论非中国团队发明；选项C范围扩大，文中只说为量子互联网铺路，未建成；选项D偷换概念，文中说理论上100公里，实际是11公里。
45. What is the best title for the text?
- A. Quantum Computers: A Threat to Modern Technology
- B. Entanglement: The Key to Future Communication
- C. DI-QKD: A New Defense Against Quantum Hacking
- D. The Development of Global Quantum Internet
答案：C
答案句：Secret codes once thought impossible to crack now face a challenge from quantum (量子) computers. Luckily, to protect information, physicists have developed a theoretically reliable system called device-independent quantum key distribution (DI-QKD), which uses entangled (纠缠的) quantum particles (粒子) to fix weak points in existing methods. Now, a team in China has demonstrated the technique in real city conditions, an advance that could clear the way for a secure quantum internet in which trust is taken for granted. … DI-QKD removes the need for trust in the hardware by employing another feature of quantum mechanics — entanglement — which closely links properties of widely separated quantum particles. … In 2022, a UK-based team managed to create and share a DI-QKD key for only about 2 meters. Now, the Chinese team led by Jianwei Pan have extended this to practically useful distances. After collecting data for 26 days, they showed they had the statistics to establish and share a key across 11 kilometers. The researchers also showed that in theory — and given about 23 years for data collection — they could have sent a key across 100 kilometers. Pan’s group now plans to explore ways to perform DI-QKD using satellites in space.
参考译文：曾经被认为无法破解的密码现在面临着量子计算机的挑战。幸运的是，为了保护信息，物理学家们开发了一种理论上可靠的系统，称为设备无关量子密钥分发（DI-QKD），它利用纠缠的量子粒子来修复现有方法中的弱点。现在，中国的一个团队在真实城市条件下演示了这项技术，这一进展可能为安全的量子互联网铺平道路，在这种互联网中，信任是理所当然的。 … DI-QKD通过利用量子力学的另一个特征——纠缠——来消除对硬件的信任需求，纠缠将广泛分离的量子粒子的属性紧密联系起来。 … 2022年，一个英国团队设法创建并共享了一个仅约2米长的DI-QKD密钥。现在，由潘建伟领导的中国团队将其扩展到实际有用的距离。在收集了26天的数据后，他们表明有统计数据可以建立并共享跨越11公里的密钥。研究人员还表明，理论上——如果数据收集约23年——他们可以将密钥发送到100公里之外。潘的团队现在计划探索使用太空卫星执行DI-QKD的方法。
定位线索：题干“best title”→全文围绕DI-QKD展开；首段“developed a theoretically reliable system called device-independent quantum key distribution (DI-QKD)”对应选项C“DI-QKD: A New Defense Against Quantum Hacking”；文中“fix weak points in existing methods”“removes the need for trust in the hardware”对应选项C中“Defense”；选项A“Quantum Computers”只是背景，选项B“Entanglement”是技术细节，选项D“Global Quantum Internet”是未来展望。
解析：题干问最佳标题，需概括全文主旨。首段提出量子计算机威胁，引出DI-QKD作为解决方案，后文详细阐述其原理和进展，故选项C“DI-QKD: A New Defense Against Quantum Hacking”准确概括。选项A“Quantum Computers”仅提及背景，非主旨；选项B“Entanglement”是DI-QKD的技术手段，非核心；选项D“Global Quantum Internet”是未来应用，范围扩大，文中未实现全球量子互联网。