题目选项分析

To map Earth's interior, geologists use a network of seismometers to chart seismic waves that originate in the earth's crust and ricochet around its interior, traveling most rapidly through cold, dense regions and more slowly through hotter rocks.

To map Earth's interior, geologists use a network of seismometers to chart seismic waves that originate in the earth's crust and ricochet around its interior, which travel most rapidly through cold, dense regions, and more slowly through hotter rocks.