在采空区建筑时,应根据地表变形特征、所处的阶段、变形值大小和上覆岩层稳定性进行建筑适宜性分区,划分出( )场地、( )场地( )场地
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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