采用关系数据模型的方法建立的数据库系统称为______。
A．对象―关系数据库系统
B．扩展关系数据库系统
C．拓展关系数据库系统
D．以上都不正确
参考答案：A
解析：采用扩展关系数据库模型的方法建立的数据库系统称作对象―关系数据库系统（ORDB），它建立 在关系数据库技术坚实的基础上，并且支持若干重要的面向对象特性，能够满足数据库新的应用需求。
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| We sometimes call the lion "the king of the jungle (丛林)" because it is stronger and more dangerous than other animals. It can 1 faster than many animals and it can hunt (捕猎) the best. It is the highest animal in the 2 food chain (食物链). In the sea, the shark is one of the animals at the 3 of the food chain. It can swim faster than 4 other sea animals, and it can use its big teeth to eat them. What is at the top of the world's food chain? 5 are! We are not the biggest or fastest, but we are the 6 . We could not run faster than cheetahs (猎豹), so we 7 cars and now we can move the fastest. We could not 8 better than lions, so we invented guns (枪). Now we can hunt the best. People's inventions are clever, but they can be 9 , too. For example, people invented 10 , and now they make the air and rivers dirty. This can make 11 hanges. Dirty rivers kill fish. 12 bears cannot eat the fish and the bears die. If we kill one part of the food chain, 13 also die. Remember that we are a part of the food chain, 14 we are in danger too! If we protect animals, we are protecting 15 ! We should and we could do something for the world! | ||||
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