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问题：
[单选题]在数据库三级模式间引入二级映象的主要作用是（ ）。
A、提高数据与程序的独立性
B、提高数据与程序的安全性
C、保持数据与程序的一致性
D、提高数据与程序的可移植性
参考答案：
A
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