Wind-propelled turbines are constructed with _________ rotor blades and a horizontal-axis turbine generator.

• A. Vertical
• B. Propeller
• C. Replaceable
• D. Retractable

Answer: (B)

The main idea is that utility-scale wind turbines use a propeller-type blade arrangement that rotates around a horizontal axis. These blades are shaped as airfoils to generate lift from the wind, turning the rotor and driving the shaft through the gearbox to the generator housed in the nacelle. This propeller-style rotor is what makes the turbine efficient at extracting wind energy at typical wind speeds.

Vertical-axis blade designs exist, but they aren’t paired with a horizontal-axis generator in the common, modern wind turbine setup, which is why the other options don’t fit. Terms like replaceable or retractable describe blade features or maintenance aspects rather than the blade geometry or axis orientation, so they’re not defining characteristics of the rotor in this context.