问题 单项选择题

在公开密钥密码体系中,______。

A.加密密钥能用来解密

B.加密密钥不能用来解密

C.加密密钥部分用来解密

D.从已知的加密密钥可以推导出解密密钥

答案

参考答案:B

解析: 在公钥加密技术中,加密密钥和解密密钥是分开的,加密密钥既不能用来解密,也不能从加密密钥推导出解密密钥。

阅读理解

阅读理解。

     Dinner customs are different around the world. If you are a guest in Ghana (加纳), this information

will help you a lot.

     In Ghana, dinner is usually from four in the afternoon to six in the evening. But there are no strict rules

about time. Whenever a guest arrives, a family offers food. When you go to a home, the person who

receives guests takes you to the living room first. At this time everyone welcomes you. Then you go to

the dinning room. There you wash your hands in a bowl of water. All the food is on the table.

     In Ghana you usually eat with your fingers. You eat from the same dish as everyone else. But you eat

from one side of the dish only. It is not polite to get food from the other side of the dish.  After dinner,  

you wash your hands again in a bowl of water.

    Most meals in Ghana have a dish called fufu. People in Ghana make fufu from the powder (粉末) of

some plants. Sometimes they cut the fufu with a saw (锯子) because it is very hard.  You must chew

fufu well, or you may get sick. You eat fufu with the fingers of your right hand only.

根据短文内容,  判断句子的正(T)误(F) 。

( )1. From the passage we know that in Ghana the rules for dinner time are not strict.

( )2. If you are a dinner guest in Ghana, the host always takes you to the dining room first.

( )3. People in Ghana usually eat with their fingers.

( )4. In fact, most dishes in Ghana are not very hard.

( )5. When you eat fufu, you'd better cut it with a saw and use your right hand and chew it well.

单项选择题