Read the passage from The Railroad Builders by John Moody. Answer the question that follows.
The railroad is sprung from the application of two fundamental ideas—one the use of a mechanical means of developing speed, the other the use of a smooth running surface to diminish friction. Though these two principles are today combined, they were originally absolutely distinct. In fact there were railroads long before there were steam engines or locomotives. If we seek the real predecessor of the modern railroad track, we must go back three hundred years to the wooden rails on which were drawn the little cars used in English collieries to carry the coal from the mines to tidewater. The natural history of this invention is clear enough. The driving of large coal wagons along the public highway made deep ruts in the road, and some ingenious person began repairing the damage by laying wooden planks in the furrows. The coal wagons drove over this crude roadbed so successfully that certain proprietors started constructing special planked roadways from the mines to the river mouth. Logs, forming what we now call "ties," were placed crosswise at intervals of three or four feet, and upon these supports thin "rails," likewise of wood, were laid lengthwise. So effectually did this arrangement reduce friction that a single horse could now draw a great wagon filled with coal—an operation which two or three teams, lunging over muddy roads, formerly had great difficulty in performing.
What is the central idea of this passage?
Horses were able to pull large coal-filled wagons with ease.
In early coal mines, wooden rails and small cars were used to carry coal from the mines to the oceans.
The coal wagons drove over this crude roadbed so successfully that certain proprietors started constructing special planked roadways from the mines to the river mouth.
The modern railway system evolved from wooden rails used to transport coal and the combination of two ideas - speed and smooth surface.