数据库管理系统常见的数据模型有层状、网状和 ______ 三种。
参考答案：关系
Only in that way _____ find out how this kind of animal lived and then finished the research on time.[ ]
A. could they
B. they could
C. did they
D. they were able to
资产评估中，实体性贬值的估算可采用( )。
A．重置核算法
B．观察法
C．价格指数法
D．功能价值法
