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:

To find the main idea, we analyze the passage. It starts by noting earthquake - related thoughts about California, then shifts to six states (Arkansas, Colorado, Kansas, New Mexico, Oklahoma, Texas plus maybe California? Wait, no, the six states are Arkansas, Colorado, Kansas, New Mexico, Oklahoma, Texas and the passage says these six states have more quakes. The key is the cause: oil and gas drilling (human activity) leads to "human - induced" quakes in these six states. The first option just states the increase in quake activity, but the passage explains the cause (oil and gas drilling) for the increase in quakes in six states. So the second option captures the main idea as it connects the cause (oil and gas drilling) to the effect (increase in quakes in six states).

Answer:

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