In modern times we humans face changing conditions.
For humans to live, we need clean air and clean water.
Pollution is now a growing problem around the world.
Pollution poisons the air and water that we depend on.
Polluted air makes people sick and afraid to go outside.
Polluted water poisons our food supply.
As a result, we never know which foods are safe to eat.
Human beings cannot live in a poisoned environment.
Therefore, pollution is a major threat to our existence.
在现代，我们人类面临着不断变化的条件。为了人类的生存，我们需要干净的空气和干净的水。污染是当今世界范围内一个日益严重的问题。污染污染了我们赖以生存的空气和水。污染的空气使人们生病，不敢出门。被污染的水污染了我们的食物供应。因此，我们永远不知道哪些食物是安全的。人类不能生活在有毒的环境中。因此，污染是我们生存的一大威胁。

Humans need temperatures to be in a comfortable range.
To be in a comfortable range means to be neither too hot nor too cold.
With global warming, global temperatures are rising.
As temperatures rise, the polar icecaps will melt.
As the polar icecaps melt, ocean levels will rise.
Areas of some countries will soon be under water.
People will be forced to relocate from flooded areas.
人类需要一个舒适的温度范围。舒适的温度范围意思是既不太热也不太冷。随着全球变暖，全球气温正在上升。随着气温升高，极地冰盖将会融化。随着极地冰盖的融化，海平面将会上升。一些国家的部分地区将很快被淹没。人们将被迫从受灾地区迁移。

In nature, even small changes can sometimes have large effects.
It's difficult to predict what's going to happen.
The entire ecosystem that we depend on is changing.
Some of these changes are irreversible.
Irreversible changes cannot be undone.
在自然界中，即使是很小的变化有时也会产生很大的影响。很难预测会发生什么事。我们赖以生存的整个生态系统正在发生变化。有些变化是不可逆转的。不可逆转的变化是无法逆转的。

Let's hope that humans are smart enough to understand how the world is changing.
With more understanding, we can make better choices about what to do.
We can face the challenges of pollution and global warming.
We need to do this before it's too late.
This planet Earth is our only home and we need to protect it.
让我们希望人类足够聪明，能够理解世界是如何变化的。有了更多的理解，我们可以更好地选择做什么。我们可以面对污染和全球变暖的挑战。我们必须在太迟之前做这件事。地球是我们唯一的家园，我们需要保护它。