Translate the following sentence into Chinese.
Many Europeans left their countries to find better conditions in America, Africa and Australia.
Because of limited resources, they choose the kind that gives the best return.
In many countries farmers find it more profitable to raise only one crop or one kind of animal.
Therefore, it would be too expensive to do all the work by hand, or to buy the equipment needed for several different kinds of farming.
At the same time, constant progress has been going on in industry.
Today, it takes only one textile worker to supervise the production of as much cotton cloth as 4,000 workers could have produced in the eighteenth century.
This productivity, however, has its price that intensive cultivation exposes the earth to the damaging forces of nature.
Such devices effectively reduce the harmful gases emitted from the engine.
The solid material, called sludge is converted into fertilizer. The sludge can also be made into bricks.
This is done in a giant compressor which can reduce a Cadillac to the size of a television set in a matter of minutes.
Agriculture is the number one industry in the United States and agricultural products are the country's leading export.
The smokestacks of these buildings should be equipped with filters and other smoke-reduction devices.
Soil erosion has become a national problem concerning everyone from the farmer to the consumer.
Controlling air pollution is another crucial objective.
Fortunately, solutions are in sight and a few of them are positively ingenious.
Corn and soybean exports alone account for approximately 75 percent of the amount sold in world markets.
We must invest more in our own people, in their jobs, in their future, and at the same time cut our massive debt.
We must do so in a world in which we must compete for every opportunity.
Our democracy must be not only the envy of the world but also the engine of our own renewal.
To preserve the very foundations of our nation, we would need dramatic change from time to time.