当下游水深小于或等于临界水深的1.3倍时,桥下为临界水流状态,此时下游天然水深不影响桥下水的出流,这种形式称为( )。
Goods are carried by several of transport--on road or rail, by sea or air.
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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