Correct Option: D

Seismometers are instrument that measures motion of the ground, including those of seismic waves generated by earthquakes, volcanic eruptions and other seismic sources. Records of seismic waves allow seismologists to map the interior of the earth and locate and measure the size of these different sources. Seismograph is another Greek term meaning to draw siesmo waves. It is often used to mean seismometer, though it is more applicable to the older instruments in which the measuring and recording of ground motion were combined than to modern systems, in which these functions are separated.