Question

human activity and earthquakes
when americans think of earthquakes, they tend to think of california, a state known for its frequent seismic activity. in recent years, however, people in arkansas, colorado, kansas, new mexico, oklahoma, and texas have been feeling the ground shake more often. an increase in oil and gas drilling in these states has led to \human - induced\ earthquakes—those resulting from human activity. when wastewater is disposed of during gas and oil drilling, the water is forced deep underground. the resulting buildup of pressure can cause fault lines (cracks in the earths crust) to shift. according to mark petersen, head of the u.s. geological surveys earthquake hazard mapping project, \in the past five years, the usgs has documented high shaking and damage in areas of these six states, mostly from induced earthquakes.\
what is the main, or central, idea of the passage?
residents of six u.s. states have experienced an increase in earthquake activity in recent years.
an increase in oil and gas drilling has caused a corresponding increase in earthquakes in six states.

Explanation:

The passage first notes increased earthquakes in six states, then explains that oil and gas drilling (human activity) causes these "human - induced" quakes by wastewater disposal creating pressure to shift fault lines. The first option only states the increase in quakes, while the second option connects the cause (oil and gas drilling) to the effect (increased quakes in six states), which is the central idea.

Answer:

An increase in oil and gas drilling has caused a corresponding increase in earthquakes in six states.