The correct answer is (a) Seismograph.
A seismograph is an instrument that measures and records the ground motion caused by earthquakes and other seismic activity. The seismograph was invented by John Milne in 1880.
A stethoscope is a medical instrument used to listen to the internal sounds of the body, chiefly the heart and lungs. It is a tube with two earpieces and a diaphragm at one end. The diaphragm is placed on the chest or other part of the body, and the doctor listens through the earpieces to hear the sounds of the heart or lungs.
A comograph is a device used to measure the speed of light. It was invented by Armand Fizeau in 1849.
A periscope is an optical instrument used to see above or around an obstacle. It is used in submarines, tanks, and other vehicles.
The correct answer is (a) Seismograph because it is the only device that is used to measure the intensity of earthquakes.