曲线未被平衡欠超高困难情况下不大于（）mm。A、30B、50C、75D、90

阅读理解。

     Mark Twain was an American writer. One day he went to a city by train. He wanted to see one of his

friends there. He was a very busy man. He usually forgot something.

     When he was in the train, the conductor asked him for his ticket. Mark Twain looked for his ticket here

and there, but he couldn't find it. The conductor knew Mark Twain. He said, "Show me your ticket on your

way back. And if you can't find it, it doesn't matter.

     "Oh, but it does," said Mark Twain, "I must find the ticket. If I can't, how can I know where I am going?"

1. Mark Twain was a _____.

A. teacher

B. farmer

C. writer

D. conductor

2. Mark Twain went to the city _____.

A. by train

B. by car

C. by air

D. by ship

3. Mark Twain went to the city _____.

A. to buy some books

B. to see his friend

C. to see his parents

D. to see a film

4. When he was in the train, the conductor asked him for _____.

A. some books

B. some food

C. some help

D. his ticket

5. Mark Twain didn't show his ticket because _____.

A. he didn't like the conductor

B. the conductor didn't ask for it

C. he couldn't find it

D. he didn't buy the ticket at all

对于急性消化道大出血患者，应放在首位的有关检查是（）。

A.是否出现呕血，以及呕血的色与量

B.是否出现便血，以及便血的性质与频率

C.是否出现周围循环衰竭的临床表现

D.是否出现贫血，以及血象的相关变化

E.以上都不是

某条形基础宽2.5m，埋深2.0m，土层分布0～1.5m为填土，γ＝17kN/m³；1.5～7.5m为细砂，γ＝19kN/m³，c_k＝0，ψ_k＝30°。地下水位地面下1.0m，试计算地基承载力特征值。

在中国生物医学文献光盘数据库（CBMdisc）的记录中出现的“AB”字段代表的是第一著者地址。

什么是数据库备份？