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问题 单项选择题

下列关于蛋白质生物合成的描述哪一项是错误的

A．氨基酸必需活化成活性氨基酸

B．氨基酸的羧基端被活化

C．体内所有的氨基酸都有相应密码子

D．活化的氨基酸被搬运到核蛋白体上

E．tRNA的反密码子与mRNA上的密码子按碱基配对原则结合

答案

参考答案：C

解析：有密码子的氨基酸只有20种，羟脯氨酸，瓜氨酸等不在20种之内的都没有密码子。其他4项描述正确。

阅读理解

阅读短文，用合适的单词完成句子。

     John is a paper boy. He delivers (送) newspapers to different houses in his street every day. He

has about 80 customers (客户). Half of his customers only take the newspapers on weekdays, and

about half take the newspapers on weekends. Two of John's customers only take the newspapers on

Sundays.

     John has to get up at 4:30 every morning to deliver his newspapers on Sundays.

     John is saving his money to buy a new bike. He is also saving money for college. He has $500 in

the bank now.

1. John delivers _____ every day.

2. John has about _____ customers.

3. _____ of his customers only take the newspapers on Sundays.

4. John is saving his money to buy _____.

5. "Paper boy" in this story means "_____ in Chinese.

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单项选择题

使用信息加密软件（）。

A．保证了数据的安全性 

B．要求手工分发密钥 

C．增加了系统的开销 

D．减少了定期变更密码的要求
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