What does the phrase 'constant of people' means?

Gold is not now being extracted from seawater. why not? a. it would be too disruptive to marine life to develop any marine mineral resources b. there is no gold in seawater c. we don't know how to extract minerals from seawater d. it would be too costly and difficult to separate the small amount of gold from the very large amounts of halite and other minerals

Me plzzz what is the ratio of water than falls on land as compared to the amount that falls onto the oceans? what role do clouds play in regulating earth’s energy balance? me plzzz

Name the two rivers that run through the fertile crescent. how were the rivers both positive and negative to societies of the fertile crescent?