Final answer:
Cotton was the most commonly grown and sold crop in eastern and southern Oklahoma in the early 1900s. It became the South's major commercial crop before the Civil War, with the invention of the cotton gin revolutionizing its production. Option a is the answer.
Step-by-step explanation:
The crop most commonly grown and sold in eastern and southern Oklahoma in the early 1900s was cotton. During the antebellum era, which is the period before the Civil War, cotton emerged as the major commercial crop in the South, surpassing tobacco, rice, and sugar in economic significance. By 1860, the southern region of the United States was producing two-thirds of the world's cotton supply. The invention of the cotton gin by Eli Whitney in 1793 revolutionized cotton production by making the process of separating seeds from raw cotton much faster and less labor-intensive. This innovation spurred the widespread cultivation of cotton, and American plantation owners found a staple crop that allowed them to compete effectively in the global market.