In which location did most of the earliest civilizations develop? plainsmountain rangestropical islandsriver valleys

- three-quarters or two-thirds..

- "the constitution provides that an amendment may be proposed either by the congress with a two-thirds majority vote in both the house of representatives and the senate or by a constitutional convention called for by two-thirds of the state legislatures."

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the answer would more than likely a.)falling crop prices  

hope the answer is right and ,either way have a nice day.