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

How does the developer of a large database system achieve(71)and data independence？ How does the developer make certain that stored items are(72)and do not simply disappear in the immensities of the database, as if in quicksand？

One solution is to set up a(73)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(74), 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(75)such differences.

A．consistency

B．identification

C．coherence

D．convergence