什么是气动比例阀:乌鸦喝水> 英语版

CROW perishing with thirst saw a pitcher, and hoping to find water, flew to it with delight.

When he reached it, he discovered to his grief that it contained so little water that he could not possibly get at it. He tried everything he could think of to reach the water, but all his efforts were in vain.

At last he collected as many stones as he could carry and dropped them one by one with his beak into the pitcher, until he brought the water within his reach and thus saved his life.

Necessity is the mother of invention.

A crow felt very thirsty, he looked for water everywhere. The crow saw a bottle, bottle water. But the bottle mouth is very high, and small, there is not much water, it can not drink. The crow saw there are many small stones. It figured out a way to. The crow put little stones one by one to the title, in the bottle, the bottle of water gradually increased, crow drinking water.