设某处工程由挖基槽、浇垫层、砌砖基、回填土四个有工艺顺序关系的施工过程组成,它们的流水节拍均为2天,若施工段数取为4段,则其流水工期为( )天。
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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