网络安全包含了网络信息的可用性、保密性、完整性和网络通信对象的真实性。其中，数字签名是对（）的保护。
A．可用性
B．保密性
C．连通性
D．真实性
参考答案：D
解析：
本题考查网络安全方面的基础知识。
数字签名(Digital Signature)技术是不对称加密算法的典型应用。数字签名的应用过程是：数据源发送方使用自己的私钥对数据校验和或其他与数据内容有关的变量进行加密处理，完成对数据的合法“签名”；数据接收方则利用对方的公钥来解读收到的“数字签名”，并将解读结果用于对数据完整性的检验，以确认签名的合法性。数字签名技术是在网络系统虚拟环境中确认身份的重要技术，完全可以代替现实过程中的“亲笔签字”，在技术和法律上有保证，可见数字签名是对签名真实性的保护。
Directions: There are 4 passages in this part. Each of the passages is followed by ,5 questions or unfinished statements. For each of them there are 4 choices marked A, B, C and D. Choose the best one and mark your answer on the ANSWER SHEET with a single line through the center.
Passage One
| In science, a theory is a reasonable explanation of observed events that are related. A theory often involves an imaginary model that helps scientists picture the way an observed event could be produced. A good example of this is found in the kinetic (运动的) molecular theory, in which gases are pictured as being made up of many small particles that are in constant motion. A useful theory, in addition to explaining past observations, helps to predict events that have not as yet been observed. After a theory has been publicized, scientists design experiments to test the theory. If observations confirm the scientists’ predictions, the theory is supported. If observations do not confirm the predictions, the scientists must search further. There may be a fault in the experiment, or the theory may have to be revised or rejected. Science involves imagination and creative thinking as well as collecting information and performing experiments. Facts by themselves are not science. As the mathematician Jules Henri Poincare said: "Science is built with facts just as a house is built with bricks, but a collection of facts cannot be called science anymore than a pile of bricks can be called a house. " Most scientists start an investigation by finding out what other scientists have learned about a particular problem. After known facts have been gathered, the scientist comes to the part of the investigation that requires considerable imagination. Possible solutions to the problem are formulated. These possible solutions are called hypotheses. In a way, any hypothesis is a leap into the unknown. It extends the scientist’s thinking beyond the known facts. The scientist plans experiments, performs calculations, and makes observations to test hypotheses. For without hypotheses, further investigation lacks purpose and direction. When hypotheses are confirmed, they are incorporated into theories. |
Which of the following statements is supported by the passage
A．A scientist’s most difficult task is testing hypotheses.
B．It is better to revise a hypothesis than to reject it.
C．Theories are simply imaginary models of past events.
D．A good scientist needs to be creative.