The largest empire of the early (pre-Columbian) American civilization was the Inca Empire. The Incas called their own empire Tawantinsuyo, meaning 'Land of the Four Quarters' or 'The Four Parts Together'.
The US may eliminate a tariff because the increase of specialization and the benefits from economy scales.
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The four main elements of the human body are oxygen, hydrogen, carbon, and nitrogen.
Major shifts, that is shifts in the paradigms, are not very frequent - they would make scientific research unstable, as any result of a smaller study could be made invalid by a paradigm shift,
minor changes however are quite common - basically every scientific study adds to the common knowledge and this also can be considered a minor change.
Therefore the best answer is
<span>Major
shifts in scientific views very rarely occur, but minor modifications
of prior knowledge are continually made based on new research.</span>
