构成数据模型的三大要素是__________、数据操作和数据完整性约束。
参考答案：数据结构
The earthquake which happened in Yushu _______ 14th April 2010 was a big disaster.[ ]
A. at
B. on
C. in
D. to
采用定压充电时，充电电压一般每个单格约2.5V
