Final answer:
Cotton was the most commonly grown and sold crop in eastern and southern Oklahoma in the early 1900s due to the region's suitable climate and soil.
Step-by-step explanation:
The crop that was most commonly grown and sold in eastern and southern Oklahoma in the early 1900s was cotton. The region's climate and soil conditions were well-suited for cotton cultivation, making it a prevalent agricultural product during that time. Cotton farming played a significant economic role and was emblematic of the broader agricultural practices in the American South.