Yesterday,we didn't have cars.But today we have.Yesterday,we didn't have TV sets.But today we have.Yesterday we didn't have computers.But today we have.During the hundreds of years,how fast the world has changed!That's really a myth.

Though the new world brings us a convenient life.It also brings more problems.For example,population,resources ,environment and so on.

We know that the world's population is growing faster and faster. It's more than 6 billion now.It's a very big number.We can say the number of world's population is like the number of the stars in the universe.And if it goes on like that,I can't image what will happen.

As the second problem,the world is short of resources now.In daily life,we need water,rock oil,coal and other things.Day after day,the resources disappear fast.And they won't appear.Because most of them are not renewable resources.

The third problem is environment.Everyone talks about it.The weather is hotter and hotter .That means we pollute the environment seriously.Our cars make the air dirty.Old batteries make the soil poisonous.Waste water makes clean water dirty.So we don't have fresh air,fecund soil and pure water.Oh,no.Stop polluting!

Now we human beings should face the new challenge .We must think more about our mother earth.Remember:We don't have another earth!