TOEFL Reading: ETS-TOEFL阅读机经 - 31FN15YFEL_J7FO8L$

According to paragraph 3, the groundwater that flows into microcracks before an earthquake causes A. changes in seismic waves and electrical activity B. increases in the mineral content of rocks C. the disappearance of grain boundaries in rocks D. a release in the tension of highly stressed areas of rocks