Correct Answer:
B. Seismograph
The question asks about the instrument used to measure earthquakes, which falls under the foundational concept of seismology. The correct answer is Seismograph.
- A Seismograph is an instrument that detects and records seismic waves generated by earthquakes, providing data on their magnitude and location.
- Barometer (Option A) is used to measure atmospheric pressure, not seismic activity.
- Hygrometer (Option C) is used to measure humidity in the atmosphere.
- Therefore, options A and C are incorrect as they measure different environmental parameters.