GIS的组成部分：（）
A、硬件
B、软件
C、数据
D、人员
E、方法
参考答案：A, B, C, D, E
Not only his parents but also his brother to the Summer Palace. They haven’t been back.
A．have been
B．have gone
C．has been
D．has gone
设关系R和S具有相同的目，且它们相对应的属性的值取自同一个域，则R-(R-S)等于______。
A．R∪S
B．R∩S
C．R×S
D．R÷S
