在完全竞争的行业中，企业的需求曲线是水平的，所以，企业的边际成本曲线也是水平的。

In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet.

How does the developer of a large database system achieve (1) and data independence How does the developer make certain that stored items are (2) and do not simply disappear in the immensities of the database, as if in quicksand

One solution is to set up a (3) system, in which all data (the internal level), all records and files (the conceptual level), and all user interfaces (the external level) are controlled by one central programming group. This may seem the most useful solution. But worldwide enterprises such as the meteorological and satellite tracking networks, IBM, and General Motors gather and record information at a very large number of locations. To stay flexible and avoid top - heaviness, such an organization might want to avoid excessive centralization.

A centralized system is (4) , but it may not be responsive to user needs. This is particularly true in a large organization - the worldwide meteorological network, for example, Data-gathering methods in the Himalayas, the equatorial jungles are different in very possible way. It is reasonable to believe that the best choices for the corresponding data storage and access structures ought to be just as different. A centralized database system would not (5) such differences.

2（）

A．usable

B．searchable

C．independent

D．retrievable

什么是“计划生育技术服务机构”？

电熔熔接机操作前，应检查电源（），确认其符合焊机要求。

A、输入功率

B、输出功率

C、电流

D、电压

个人住房贷款业务信用风险涉及购房人和( )两方面。

A．政府

B．建造商

C．开发商

D．物业管理企业