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问题 单项选择题

下列选项中，关于加密与解密算法的描述不正确的是( )。

A．加密算法是相对稳定的
B．解密算法所使用的密钥称为解密密钥
C．加密算法一定要做好保密工作
D．对密文解密时采用的一组规则称为解密算法

答案

参考答案：C

解析： 对明文进行加密时采用的一组规则称为加密算法。对密文解密时采用的一组规则称为解密算法。加密算法和解密算法通常都是在一组密钥控制下进行的，加密算法所使用的密钥称为加密密钥，解密算法所使用的密钥称为解密密钥。加密算法是相对稳定的。在这种意义上，可以把加密算法视为常量，而密钥则是一个变量。加密算法实际上很难做到绝对保密，因此现代密码学的一个基本原则是一切秘密寓于密钥之中。

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单项选择题

(二)


"Sesame Street" has been called "the longest street in the world". That is because the television program by that name can now be seen in: so many parts of the world. That program became one of American’s exports soon after it went on the air in New York in 1969.
In the United States more than six million children watch the program regularly. The viewers include more than half the nation’s preschool children, from every kind of economic, racial, and geographical group.
Although some educators object to certain elements in the program, parents praise it highly. Many teachers also consider it a great help, though some teachers find that problems arise when first graders who have learned from "Sesame Street" are in the same class with children who have not watched the program.
Tests have shown that children from all racial, geographical, and economic backgrounds have benefited from watching it. Those who watch it five times a week learn more than occasional viewers. In the US the program is shown at different hours during the week in order to increase the number of children who can watch it regularly.
The programs all use songs, stories, jokes, and pictures to give children a basic understanding of numbers, letters and human relationships. But there are some differences. For example, the Spanish program, produced in Mexico City, devotes more time to teaching whole words than to teaching separate letters.
Why has "Sesame Street" been so much more successful than other children’s shows Many reasons have been suggested. People mention the educational theories of its creators, the support by the government and private businesses, and the skillful use of a variety of TV tricks. Perhaps an equally important reason is that mothers watch it along with their children. This is partly because famous adult stars often appear on it. But the best reason for: the success of the program may be that it makes every child watching feel able to learn. The child finds himself learning, and he wants to learn more.

What is special about the program

A．It offers great fun.

B．It makes children feel able to learn.

C．It is shown at different hours during the week.

D．Children learn and enjoy themselves while watchin
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