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问题 单项选择题

下列关于空值的叙述中，正确的是( )。

A．空值是双引号中间没有空格的值

B．空值是等于0的数值

C．空值是使用Null或空白来表示字段的值

D．空值是用空格表示的值

答案

参考答案：C

解析： 在数据库中，空值用来表示实际值未知或无意义的情况。任何数据类型的列，只要没有使用非空(NotNull)或主键(Primary Key)完整性限制，都可以出现空值。

多项选择题

稳定型心绞痛与急性心肌梗死的鉴别要点是（）

A.疼痛时间

B.白细胞计数

C.疼痛性质

D.疼痛部位

E.心肌坏死标记物
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单项选择题

Attempts to understand the relationship between social behavior and health have their origin in history. Dubos (1969) suggested that primitive humans were closer to the animals (1) they, too, relied’upon their instincts to stay healthy. Yet some primitive humans (2) a cause and effect relationship between doing certain things and alleviating (3) of a disease or (4) the condition of a wound. (5) there was so much that primitive humans did not (6) the functioning of the body, magic became an integral component ofthe beliefs about the causes and cures of heath (7) Therefore it is not (8) that early humans thought that illness was caused (9) evil spirit. Primitive medicines made from vegetables or animals were invariably used in combination with some form of ritual to (10) harmful spirit from a diseased body.

One of the. earliest (11) in the Western world to formulate principles of health care based upon rational thought and (12) of supernatural phenomena is found in the work of the Greek physician Hippocrates. The writing (13) to him has provided a number of principles underiying modern medical practice. One of his most famous (14) , the Hippocratic Oath, is the foundation of contemporary medical ethics.

Hippocrates also argued that medical knowledge should be derived from a (15) of the natural science and the logic of cause and effect relationships. In this (16) thesis, On Air, Water, and Places, Hippocrates pointed out that human well-being is (17) by the totality of environmental (18) : living habits or lifestyle, climate, geography of the land, and the quality of air, and food. (19) enough, concerns about our health and the quality of air, water, and places are (20) very much written in twentieth century.

17（）

A.impressed

B.surpassed

C.influenced

D.regarded
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