问题 填空题

由关系数据库系统支持的完整性约束是指______和参照完整性。

答案

参考答案:实体完整性。

解析: 关系的完整性约束指关系的某种约束条件,包括实体完整性、参照完整性和用户定义的完整性。其中,前两种完整件约束由关系数据库系统自动支持。

阅读理解

阅读与表达。

     Happiness is U-shaped, for we are happier at the start and end of our lives but hit a slump (低潮) when

we are middle-aged, scientists from England and America say. They have studied the information on the

mental (心理的) health of two million people from 80 countries.

     In England, the probability of low spirits for men and women reaches the highest point at around 44 years

of age. In America, though, there is a big difference between men and women. Among women, unhappiness

reaches the highest point at around the age of 40, but among men, it is about 50.

     But the U-shape of happiness is unchanging around the world, and the mid-life sadness happens regardless

of marital status (婚姻状况), changes in jobs or pay. It happens to men and women, to single and married

people, to rich and poor, and to those with and without children.

     One possibility may be that people realize many of their dreams won't come true at middle age. The

researchers said another reason could be that seeing their middle- aged friends die one by one, people begin to

value their own remaining years and their Iove of the nature and long for peaceful and free life once more.

     But the good news is that if people make it to aged 70 and are still physically fit, they are on average (平均)

as happy as a 20-year-old person. For the average people in the modem world, the fall in mental health and

happiness doesn't come on suddenly in a single year. Only in their fifties do people get out of this low period.

1. Do people feel happy at the start and end of their lives?

    _____________________________________________________________________________________

2. Where are the scientists in the passage from? 

    _____________________________________________________________________________________

3. When does the unhappiness reach the highest point among men in America, at the age of 40 or about 50?

    _____________________________________________________________________________________

4. What is the good news for a 70-year-old healthy man? 

    _____________________________________________________________________________________

5. How will a teenager feel in his future life according to the passage? 

    _____________________________________________________________________________________

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