如图有一输水管道,水自截面1-1流向截面2-2。测得截面1-1的水流平均流速u1=2m/s,已知d1=0.5m, d2=1m,截面2-2处的平均流速为( )
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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