题目选项分析

Seismologists studying the earthquake that struck northern California in October 1989 are still investigating some of its mysteries：the unexpected power of the seismic waves,the upward thrust threw one man straight into the air, and hours before the temblor strange electromagnetic signals were detected.

Seismologists studying the earthquake that struck northern California in October 1989 are still investigating some of its mysteries：the unexpected power of the seismic waves,the upward thrust that threw one man straight into the air, and the strange electromagnetic signals detected hours before the temblor.