An impeller is described as having which feature?

• A. Multiple moving parts, complex controls
• B. No moving parts
• C. Requires gears to operate
• D. One moving part, efficient, simple controls

Answer: (D)

An impeller moves fluid by a single rotating element with blades attached to a hub. This design means there’s essentially one moving part doing the work, which makes the system compact and efficient. With just one rotating piece, there’s less mechanical complexity, so controls can be simple—you’re not coordinating gears or multiple moving parts. If there were no moving parts, it couldn’t move the fluid; if it relied on gears or many moving parts, it would be more complex and less efficient. So describing it as having one moving part, while being efficient and easy to control, is the best fit.