6. the average copper ore mined in 1900 was five percent copper by weight. copper ore mined in 1990 was approximately 0.5 percent copper by weight. what factors could account for this difference? "

The volume of miners and industries using copper in the 20th century presented an exponential growth. Mining tends to extract the highest grade resources first, once they are the most profitable. With the intense activity achieved during the last century, the higher grade non renewable sources were quickly depleted, forcing the industry to start exploring lower grades sources to satisfy the demand.

It is also noteworthy that mining copper of higher quality causes more damage to the environment, having its protocols and restrictions consequently addressed by the legislation. Therefore the costs of mining 5% copper might be outweighed by a higher margin of profit from 0.5% copper which also is less damaging to the environment.

a.

congress passed laws allowing for free passage between states.

the correct option is: a liberal.

the kind of person that is most likely to hold a left-wing political ideology is liberal because they have in common that they support human individual rights and liberties. also, they both have politically and economically centrist.

moreover, a liberal believes that everyone should have equal rights as well as opportunities to succeed in life, and the freedom to make their own decisions as long as they don't attack the rights of other people. all people deserve the same opportunities and basic needs.