问题 单项选择题

在并发控制中引入两段锁协议的目的是

A) 为了解决并行执行时可能引起的死锁问题
B) 为了解决并行执行时可能引起的活锁问题
C) 为了解决交叉调度的不可串行化问题
D) 为了解决不同的调度导致不同的运行结果

答案

参考答案:C

解析: 两段锁协议是指所有事务必须分两个阶段:
第一阶段是获得封锁,也称为扩展阶段;第二阶段是释放封锁,也称为收缩阶段。
若并发执行的所有事务均遵守两段锁协议,则对这些事务的任何并发调度策略都是可串行化的。

阅读理解

As the semester(学期) ended, students had a chance to turn the tables on their teachers.

They got to grade me anonymously(匿名地), assessing the ability of my thinking, my organizational skills and the depth of my knowledge. Such evaluations keep me alert to what works and what doesn’t. Students reflect my performance back to me, and I’m glad to learn what they think of my teaching so that I might try to improve.

This system reflects many aspects of my work. There is, of course, nothing wrong with it. But this system assumes that what students need is the same as what they want. Reading my evaluations every semester has taught me otherwise. Actually many students’ expectations for their courses have already changed, reflecting, in part, the business model many universities are following: classes are considered services, and parents are eager to get their money’s worth from their children’s education. Students feel pressure from their parents to get practical use from their courses.

This could make sense for an engineering course, but in my field, creative writing, which rarely trains up excellent 21-year-old writers, it is more difficult to provide the results that the career-minded students desire. Then I tried some teaching techniques to change the criticism of those unhappy students to the opposite and improve my student evaluations. My record would accurately reflect a smart, attentive, encouraging teacher. However, I would admit that they loved me simply because I agreed writing should be easy.

I know other teachers have done the same thing: teach your heart out to the teachable but be sure to please the unteachable; keep your ratings high, like a politician trying to improve his poll(民意调查) results. I believe in the struggle. But I still can’t help wincing(退缩) when I read, “The instructor is mean.” “Marcus is not committed to my work.” “This class sucks.” The business model has taught me that customers are always right. And maybe a few more dissatisfied customers would mean a better learning experience.

小题1:What can we know from the underlined phrase “turn the tables on their teachers”?

A.Students get a chance to have dinner with their teachers.

B.Students judge and grade their teachers.

C.Students begin to criticize and punish their teachers.

D.Students take action to praise their teachers.小题2:Why have the students’ expectations for their courses changed?

A.Because students want to improve other abilities.

B.Because students feel great pressure from universities.

C.Because students have to satisfy their parents.

D.Because the business model has changed.小题3:What can we infer from the passage?

A.Parents don’t care about their money spent on their children’s education.

B.The writer adopted some teaching methods so that he improved his student evaluations.

C.Similar to other teachers, the writer struggled to work as politicians.

D.The students intended to punish their teachers by giving comments.小题4:What is the author’s attitude towards being graded by his students?

A.Positive.

B.Negative.

C.Satisfied.

D.Scared.

单项选择题