Read this excerpt from The Great Fire. As the rest of the city went about its business, fireman Dorsey was racing through the streets to the closest signal box, which happened to be at Goll's drugstore. He opened the small door on the box and used his thumb to pull down the lever. Dorsey then headed back to the scene of the fire, not realizing that he'd made a mistake — he had forgotten to pull down the lever four times, a special signal that would have made it a true second alarm. At the Courthouse, Schaffer and Brown would hear Dorsey's alarm, but, assuming it was simply another signal telling them about the original fire, they failed to call out more engines.

How does this excerpt support the main idea of the passage?

It illustrates how many mistakes firefighter Dorsey made during the course of the fire.
It demonstrates how the city’s fire alarm system and signal boxes worked.
It describes one of the key mistakes that prevented the fire from being extinguished sooner.
It highlights the fact that Bruno Goll was responsible for the fire and stopped it from being put out.