Answer:
The main reason for building Hoover Dam was to supply the electrical power necessary to transport 4.4 million acre-feet—over a quarter of the Colorado River's average annual flow—to California.
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it will take 3000 days because it takes long
In reality it was the Mesopotamians, but other sources say it was Sumerians, since it's on your list.
Explanation:
There are 100 Senators in the US Senate. 2 Senators are chosen every 6 years.