问题 单项选择题

数据库系统的并发控制主要方法是采用哪种机制
A) 拒绝
B) 可串行化
C) 封锁
D) 不加任何控制

答案

参考答案:C

解析:解析:数据库中的数据是宝贵的共享资源,用户可以并发使用数据,这样,必须有一定的控制手段来保障资源免于破坏。数据库管理系统对事务的并发执行进行控制,以保证数据库一致性,最常用的方法是封锁的方法,即当一个事务访问某个数据项时,以一定的方式锁住该数据项,从而限制其事务对该数据项的访问。

阅读理解

阅读理解。

     It's known to us that when we taste delicious food, some people are in hunger. They live a hard life. They are poor and always don't have enough food to eat.

     Food banks are the organizations to help these poor people. Food banks receive the food from companies or supermarkets, and also from donations from the public. In this way, they collect extra food and give out the food to people who are hungry.

     The first food bank was St. Mary's Food Bank. It started in 1967 in Arizona. In 1979, it became a larger organization named America's Second Harvest Network-made up of over 200 food banks across the USA. Each year, the Network provides food for more than 25 million hungry people in the United States, including more than 9 million children and nearly 3 million old people.

      Volunteers are important to food banks. There are many different ways for you to volunteer. You can help out through activities such as:

     *Sorting, boxing and packaging donated food.

     *Tutoring poor kids at your local Kids Café.

     *Transporting or delivering food.

      It's simple. Take part in it today, and let's try to make our world without hunger!

1. We can learn from the passage that food banks are _____.

A. some special banks

B. some organizations

C. the banks for poor people

D. the banks to receive food

2. What is the meaning of the underlined word"donations"?

A. something given

B. extra food

C. the Network

D. volunteers

3. It can be inferred from the last paragraph that _____.

A. the author wants to set up another food bank

B. many young people want to become volunteers

C. few people want to become volunteers

D. the author hopes to see more people become volunteers

4. What would be the best title for this passage?

A. Help the people in hunger

B. Go to become volunteers

C. Food banks

D. Make our world without hunger

单项选择题