Final answer:
The most accurate timepiece before the mechanical clocks was the Egyptian water clock, or clepsydra, which used the regulated flow of water to measure time.
Step-by-step explanation:
The Egyptian water clock was the most accurate timepiece in the world until the invention of mechanical clocks in medieval Europe. The correct answer to this question is c) Water clock. Water clocks, also known as clepsydras, measured time based on the regulated flow of water from or into a vessel.
Water clocks were among the earliest timekeeping devices that didn't depend on the observation of celestial bodies. Some of the very first water-powered clocks in China worked by the gradual filling or draining of a container with water that in turn operated a mechanical device to show the time.
Accuracy in timekeeping has greatly evolved over the years. While sundials were common and used in various iterations throughout history, including the simple vertical stick sundial, the invention of the water clock provided a more consistent measurement that was less affected by weather conditions.