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分析某地麻疹患者年龄构成，显示主要集中在学龄儿童(单峰)，提示
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数据模型定义了数据库系统中数据组织、存储和管理必须遵循的规范，可以分为概念数据模型、数据结构模型和物理数据模型三大类。其中概念数据模型的典型代表是
需求包括许多方面的内容。其中，描述系统中数据定义以及数据间的联系属于下列哪方面的内容
在下列各种编码中，每个字节最高位均是“1”的是( )。
During recent years we have heard much about "race": how this race does certain things and that race believes certain things and so on. Yet, the (21) phenomenon of race consists of a few surface indications.We judge race usually (22) the coloring of the skin: a white race, a brown race, a yellow race and a black race. But (23) you were to remove the skin you could not (24) anything about the race to which the individual belonged. There is (25) in physical structure, the brain or the internal organs to (26) a difference.There are four types of blood. (27) types are found in every race, and no type is distinct to any race. Human brains are the (28) . No scientists could examine a brain and tell you the race to which the individual belonged. Brains will (29) in size, but this occurs within every race. (30) does size have anything to do with intelligence. The largest brain (31) examined belonged to a person of weak (32) .On the other hand, some of our most distinguished people have had (33) brains.Mental tests which are reasonably (34) show no differences in intelligence between races. High and low test results both can be recorded by different members of any race. (35) equal educational advantages, there will be no difference in average standings, either on account of race or geographical location. Individuals of every race (36) civilization to go backward or forward. Training and education can change the response of a group of people, (37) enable them to behave in a (38) way.The behavior and ideals of people change according to circumstances, but they can always go back or go on to something new (39) is better and higher than anything (40) the past. 38().
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