The best answer is B. the prohibition of sharecropping by freedmen in Indian Territory.
This option is not a motivation for African Americans migrating to Oklahoma, as sharecropping was a prevalent practice among freedmen in the South, and there was no prohibition against it in Indian Territory at the time. The other options reflect motivations for migration, including the desire for self-determination, escaping Jim Crow laws, and seeking economic opportunities in the form of land.