Question

read the text.
the greatest dam in the world
1 hoover dam is a massive concrete dam on the colorado river, sitting at the border of arizona and nevada. before the building of hoover dam, the colorado river was dangerous and unreliable. melting snow in the mountains caused damaging floods during the late spring and early summer. unpredictable flash floods could occur in any season. but by midsummer, the rivers flow was barely enough to supply the farms in southern california and arizona that depended on it.
2 in 1905, the colorado river flooded what had been rich, irrigated farmland in the imperial valley in southern california. it caused enormous damage
what is the main focus of the text?
a technical description of the hoover dam
the significance of the hoover dam during the great depression
the history and construction of the hoover dam
the costs and challenges of the hoover dam

Explanation:

1. Analyze Option 1: The text does not give a technical description (like materials, engineering specs) of Hoover Dam. It focuses on the river's state before the dam. Eliminate this.
2. Analyze Option 2: The text has no mention of the Great Depression or the dam's significance during that time. Eliminate this.
3. Analyze Option 3: The text talks about the Colorado River's problems (floods, unreliable flow) before Hoover Dam was built, and a flood event in 1905. This sets the context for why the dam was built, relating to its history and the need for its construction. This option fits.
4. Analyze Option 4: The text does not discuss costs or construction challenges of the dam. It focuses on the river's issues pre - dam. Eliminate this.

Answer:

the history and construction of the Hoover Dam