系统的基本属性包括哪些方面()
A．层次性
B．统一性
C．整体性
D．相关性
E．目的性
参考答案：A, C, D, E
Why is Venice san sinking
A．Because people only stop using underground water for industries on the mainland.
B．Because people still make use of the underground water for all purposes.
C．Because the use of groundwater far industries on the mainland has been stopped.
D．Because people do not use the underground water any more.
甲、乙两物体都做匀速直线运动，它们通过的路程之比为2：1，所用时间之比为2：3，则速度之比为 [ ]
A．3：1
B．1：3
C．3：4
D．4：3
