Question

read the passage.
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 mentions that people in six U.S. states (Arkansas, Colorado, Kansas, New Mexico, Oklahoma, and Texas) are experiencing more earthquakes. Then it explains that an increase in oil and gas drilling (which leads to wastewater disposal and pressure buildup causing fault - line shifts) is the cause. The second option directly connects the cause (increase in oil and gas drilling) with the effect (increase in earthquakes in the six states), which is the main idea. The first option only states the effect (increase in earthquake activity) without the cause, so it is not the main idea.

Answer:

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