Very small time intervals are accurately measured by the

The correct answer is C) Atomic Clocks.

Atomic clocks are devices that use the vibrations of atoms, typically cesium or rubidium atoms, to accurately measure time intervals. They are considered the most accurate time-keeping devices available and can measure time intervals to within a few billionths of a second. Atomic clocks are used in a variety of applications, such as satellite navigation systems, scientific research, and telecommunications networks.