问题 单项选择题

装卸危险货物时,船吊的实际负荷量不得超过其额定安全负荷量的()。

A.55%

B.60%

C.75%

D.80%

答案

参考答案:C

阅读理解

阅读理解。

     Peter is thirteen years old.  He is in Grade Two this year.  He likes to watch football matches.

And he often reads newspapers. He does his best to know where and when there is going to be a

football match.  Now Peter is having lunch.  He is listening to the radio,  too.  Hc is vcry happy

because there is going to bc a nice football match on TV at four this afternoon.

       He wants to watch it very much.  But he is going to have English and Chinese lessons.  He thinks

hard and finds a way.

       "Hello,  Mrs Black,"  Peter says to his teacher ori the telephone,  "Peter is ill in bed. He wants to

ask for half a day's lcave. "

     "Oh, I'm sorry to hear that," says Mrs Black. 'But who's that? "

      "It's my father,  Mrs I31ack. "

1.  Peter is a _____.         

A.  micidlc school student              

B.  Young Pioneer

C.  worker                    

D.  teacher

2.  Pcter will be in  _____ next year.      

A. Grade One    

B. Gracle Two    

C. Grade Three  

D. Grade Four

3.  Peter often reads newspapers because _____.          

A.  he likes to read news

B.  he likes to read stories

C.  he wants to know where and when there is going to be a football match

D. his father wants him to read them

4.  Peter wants to ask for half a day's leave because_____ .         

A.  his father is ill in bed

B.  he wants to watch the football match

C.  he doesn't like to have English and Chinese lessons

D.  he is ill in bed

5.  Which sentence is RIGHT?   

A.  Mrs Black is going to take Peter to see a doctor.

B.  Peter likes to watch TV at four in the afternoon.

C.  Peter is a stupid boy.

D.  Peter isn't an honest boy.

单项选择题 共用题干题

在数据库系统中,“事务”是访问数据库并可能更新各种数据项的一个程序执行单元。为了保证数据完整性,要求数据库系统维护事务的原子性、一致性、隔离性和持久性。针对事务的这4种特性,考虑以下的架构设计场景:假设在某一个时刻只有一个活动的事务,为了保证事务的原予性,对于要执行写操作的数据项,数据库系统在磁盘上维护数据库的一个副本,所有的写操作都在数据库副本上执行,而保持原始数据库不变,如果在任一时刻操作不得不中止,系统仅需要删除副本,原数据库没有受到任何影响。这种设计策略称为(1)。事务的一致性要求在没有其他事务并发执行的情况下,事务的执行应该保证数据库的一致性。数据库系统通常采用(2)机制保证单个事务的一致性。事务的隔离性保证操作并发执行后的系统状态与这些操作以某种次序顺序执行(即可串行化执行)后的状态是等价的。两阶段锁协议是实现隔离性的常见方案,该协议(3)。持久性保证一旦事务完成,该事务对数据库所做的所有更新都是永久的,如果事务完成后系统出现故障,则需要通过恢复机制保证事务的持久性。假设在日志中记录所有对数据库的修改操作,将一个事务的所有写操作延迟到事务提交后才执行,则在日志中(4),当系统发生故障时,如果某个事务已经开始,但没有提交,则该事务应该(5)。

空白(5)处应选择()

A.重做

B.撤销

C.什么都不做

D.抛出异常后退出