房地产周期循环的原因有（）。

A.供需因素的影响

B.供需调整不均衡存在的时滞

C.政策因素的影响

D.房地产价格从长期看呈螺旋上升的影响

E.制度因素的影响

The main feature of (72) is that they follow a first-come/first-served rule. For instance, the line of (73) waiting to be run on a computer system.

A．looplinks

B．queues

C．stacks

D．trees