And, since average swimming speed is about 3kph (2mph) even a single rescue mission can take more than half an hour.
而且，由于平均游泳速度约为3千米每小时(2英里每小时)，所以单单一项拯救任务就要耗费半个多小时。
How long does it take you to do your homework every day? About half an hour.
你每天做作业要花多长时间？大约半小时。
How long does it take you to do your homework every day? About half an hour.
你每天做作业要花多长时间？大约半小时。
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