阅读理解 阅读下列短文，选出最佳答案。
“I will think of it.” It is easy to say this, but do you know what great things have come from thinking?
Sir Isaac Newton was sitting in his garden when he saw an apple fall from a tree. He began to think and tried to find out why the apple fell. Then he discovered how the sun, moon, and stars are kept in their places.
A boy named James Watt sat quietly by the fire, watching the lid of the kettle move up and down. He wanted to find out why the steam in the kettle moved the lid. From that time he went on thinking and thinking. And when he became a man, he improved the steam engine (蒸汽机) so much that it could easily do the work of many horses.
James Ferguson was a poor boy. Once, seeing the inside of a watch, he wondered. “Why should I not make a watch?” But how could he get the materials to make the mainspring (钟表的主发条)? He soon found he could make it with whalebone (鲸骨). He then made a wooden clock which kept good time. His motto (座右铭) was “I will think of it.” And he made his thoughts useful to himself and the world.
Boys and girls, when you have a difficult lesson to learn, don't lose heart, and don't ask someone for help before helping yourselves. Think, and by thinking you will learn how to think to some purpose.
