问题
单项选择题
在数据库的三级模式结构中,外模式有( )。
A.1个
B.2个
C.3个
D.任意多个
答案
参考答案:D
在数据库的三级模式结构中,外模式有( )。
A.1个
B.2个
C.3个
D.任意多个
参考答案:D
Li Shizhen was born in 1518. His father was a poor doctor小题1: He decided to study medicine so that he could help people who were ill. Li Shizhen read many books about medicine. 小题2: So he wished to write a new one. 小题3: He studied not only the herbs(草药) in his own garden, but also the wild ones. He always went on long journeys to collect herbs and talked with old peasants. 小题4: After many years of hard work and study, 小题5: At that time he was sixty. His book is now one of the greatest contributions of the Chinese people to the medical science of the world.
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