Answer:
(C) interior, traveling most rapidly through cold, dense regions and more slowly
Explanation: Seismometers are instruments used to measure movements on the earth surface such as Earthquakes and volcanic eruptions and measure the interior of the Earth. Seismometers are capable of responding to up-down movements,the mass attached to it doesn't move due to the force of inertia.
seismometers are also used to chart/monitor or measure seismic waves that originate in the earth's crust and ricochet around its interior, most rapidly traveling through cold, dense regions and slower through hotter rocks.