洄游
是指有些鱼类在一定时期,依一定的路线,成群结队地向一定的繁殖场,越冬场或肥育场作周期性的迁游,如大、小黄鱼等。
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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