大雁是一种群栖的动物，经常成群出现。
Wild geese are a kind of social animal, they always appear in groups.
与此相反的是，受教育水平低的女性总是成群出现。
By contrast, many of America's least-educated women live in neighbourhoods where single motherhood is the norm.
抹香鲸通常被发现成群出现，每群大约有15至20条。
Sperm whales are often spotted in groups (called pods) of some 15 to 20 animals.
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