Another amazing example of survival is the salmon.另一个令人惊奇的生存例子是鲑鱼。
Salmon spend most of their lives in the ocean, which is saltwater.鲑鱼大部分的生命都在海洋中度过，海洋是咸水。
Yet, when it's time to breed, they do so in freshwater rivers.然而，当繁殖的时候，它们会在淡水河流中繁殖。
Salmon can adapt their bodies to survive in both saltwater and freshwater.鲑鱼能使它们的身体适应在盐水和淡水中生存。
When it's breeding time, they return to the same river where they were born.到了繁殖期，它们会回到它们出生的那条河。
it seems as if they have a built-in map that guides them for hundreds of miles.他们似乎有一张内置的地图，可以指引他们走几百英里。
Where do salmon spend most of their lives? in the ocean鲑鱼一生中大部分时间在哪里度过?在海洋里
Once they leave the saltwater, they don't eat.一旦离开盐水，它们就不吃东西了。
They are determined to finish their journey, despite the many obstacles.尽管有许多障碍，他们还是决心完成他们的旅程。
They swim against strong currents, jump over waterfalls and try to escape the claws of hungry bears.它们逆流而上，跳过瀑布，试图逃脱饥饿熊的爪子。
Many die along the way, but enough of them survive to breed and produce the next generation.许多人在途中死去，但他们中有足够的鱼存活下来繁衍下一代。
Once they have laid their eggs, they die, having completed their journey.一旦它们下蛋，它们就死了，完成了它们的旅程。
It seems that their purpose in life is just to reproduce.似乎它们生活的目的就是繁衍后代。
What did they do after laying their eggs? they die它们下蛋后做了什么?他们死
Migration takes animals to new, more favorable environments when the seasons change.当季节变化时，迁徙把动物带到新的、更有利的环境中。
Some of these journeys are long and dangerous, along routes with no obvious landmarks.有些旅程漫长而危险，沿途没有明显的地标。
The longest migration is that of the arctic tern.最长的迁徙是北极燕鸥。
It flies from pole to pole, twice a year.它从一个极点飞到另一个极点，一年两次。
If a tern achieves its average lifespan of 20 years, the distance it has flown will be equivalent to a journey to the moon and back.如果燕鸥的平均寿命达到20年，那么它飞行的距离将相当于一次往返月球的旅程。
A landmark is something easy to see and remember, like a river or bay.地标是一些容易看到和记住的东西，比如河流或海湾。
Humans also migrate, but seldom if ever for seasonal variations.人类也会迁徙，但很少会因为季节的变化而迁徙。
Unfortunately, human migrations are often due to human activities.不幸的是，人类迁徙往往是由于人类活动。
Since the beginning of the 21st century, large scale migrations have become a global problem.进入21世纪以来，大规模的移民已经成为一个全球性的问题。
Millions of migrants have had to leave their countries and look for new homes.数以百万计的移民不得不离开他们的国家去寻找新的家园。
Many have died along the way or lived as refugees in camps until they are admitted into a new country.许多人在被允许进入一个新国家之前，在途中死亡或在难民营中作为难民生活。
So the question remains as to how our global community will face these challenges.因此，问题仍然是我们的全球社会将如何面对这些挑战。
Most human migrations are due to human activities.大多数人类迁徙都是由人类活动引起的。
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