Reasons that human populations historically have settled in floodplains include which of the following: A. The soil in the floodplain is usually fertile B. The terrain in floodplains tends to be flat C. Floodplains are close to rivers for transportation

 A. The soil in the floodplain is usually fertile

Explanation:

A floodplain can be defined as the flat area which is expected to receive the heavy flow of water due to neighboring water body, which may cause flood. Such floodplains have been proved to be the sites of agriculture since decades due to the rich and fertile soil. As the river or any other water body brings sediments which include essential minerals supporting the growth of the crops. This will solve the problems of daily food needs for the people being settled at the neighboring places.