Excerpt from Energy from the Wind
Li Yung

3Wind is one of the oldest sources of energy. People have used the wind’s power since the beginning of recorded time. Over 5,000 years ago, ancient Egyptians used wind to sail ships on the Nile River. Later, people built windmills, thin buildings with spinning blades that are turned by the wind. When the wind turns the blades, the movement powers simple machines that can grind wheat, cut wood, or help with other tasks. For example, in the United States, people built thousands of windmills in the West that pumped water for farms and ranches.

4Today’s wind machines are a lot like the old-fashioned windmills. These machines, called turbines, use blades to collect the wind’s energy. Instead of using that energy for simple tasks, though, turbines turn the energy into electricity. Today’s wind machines are built on huge towers that are hollow and made of strong steel. The blades, called rotors, are made of tough, light materials called fiberglass and polyester. Here’s how the wind machine works. The wind pushes on the blades, making them turn. The turning blades spin a shaft that is connected to a generator, a machine that makes electricity. This electricity is then sent along wires to homes, businesses, and schools. It is used to power all sorts of tools and machines, from computers to can openers.

5Wind turbines are very striking and impressive to see. The most common type of turbine has blades like airplane propellers. Turbines stand twenty stories tall and have three blades that are each two hundred feet long. The largest wind turbine in the world, located in Hawaii, has blades that are longer than a football field!

6You may also see many wind turbines together in one area. People often build the turbines close together in a wind-power plant called a wind farm. A large wind farm may consist of a few dozen to about one hundred wind machines. One of the largest wind farms in the United States is in Altamont Pass, California. It has more than 900 wind turbines! Wind farms are built in flat, open areas where the wind blows at least twelve miles per hour.
If you were writing a research paper about wind turbines, which sentence from the passage would be irrelevant to your research?
A) The most common type of turbine has blades like airplane propellers.
B) Over 5,000 years ago, ancient Egyptians used wind to sail ships on the Nile River.
C) People often build the turbines close together in a wind-power plant called a wind farm.
D) Instead of using that energy for simple tasks, though, turbines turn the energy into electricity.