Which best explains why runoff is important?

A portion of the precipitation seeps into the ground to replenish Earth's groundwater. Most of it flows downhill as runoff. Runoff is extremely important in that not only does it keep rivers and lakes full of water, but it also changes the landscape by the action of erosion.

500 books can be produced by one man and a printing press within 5 months, while a copyist can only produce one in the same amount of time