Which invention is an accurate timekeeping device featuring a rotating wheel?

• A. Paper money
• B. Mechanical clock
• C. Silk Road
• D. Camel Caravans

Answer: (B)

Identifying a timekeeping device that uses gears and a rotating wheel is the key idea. A rotating wheel is central to mechanical clocks, where gear trains and an escapement regulate the release of energy so the hands move at a steady rate. In medieval China, innovations like Su Song's clock tower used a water-driven mechanism to turn a wheel with gears, producing regular time signals and even automated features. The other options describe currency, a trade route, and transport—not devices for measuring time. So the mechanical clock is the correct choice.