Read the excerpt from "A Byte Out of History.”

The FBI learned of the crime in flight and immediately opened an extensive investigation that lasted many years. Calling it NORJAK, for Northwest hijacking, we interviewed hundreds of people, tracked leads across the nation, and scoured the aircraft for evidence. By the five-year anniversary of the hijacking, we’d considered more than 800 suspects and eliminated all but two dozen from consideration.

Who was Cooper? Did he survive the jump? And what happened to the loot, only a small part of which has ever surfaced?

It’s a mystery, frankly. We’ve run down thousands of leads and considered all sorts of scenarios. And amateur sleuths have put forward plenty of their own theories. Yet the case remains unsolved.

What best describes the author’s purpose for this selection?

The author wants readers to understand how the FBI names its cases.
The author wants readers to understand how much effort the FBI put into solving the case.
The author wants readers to understand why the FBI was determined to figure out who Cooper was.
The author wants readers to understand when the FBI decided to stop investigating the hijacking.

The author wants readers to understand how much effort the FBI put into solving the case.

The best description of the author's purpose for this selection is that the author wants readers to understand how much effort the FBI put into solving the case. This can be inferred from the excerpt in which the author describes the extensive investigation conducted by the FBI, including interviewing hundreds of people, tracking leads across the nation, and considering over 800 suspects over the course of many years. The author's mention of running down thousands of leads and the fact that the case remains unsolved also suggests the level of determination and effort put forth by the FBI.

The best description of the author's purpose for this selection is:

The author wants readers to understand how much effort the FBI put into solving the case.