The best answer of the options that you have given us is A. The major purpose of the March on Washington was to get more support for the Civil Rights Movement.
The organizers of this march were not unemployed African Americans. Instead, the march was organized by people from many different organizations. The march was first proposed, for example, by a labor union leader, not an unemployed person or advocate for the unemployed.
The Nation of Islam did not really support the March on Washington. Malcolm X criticized it, for example, because of the fact that it included white people. This went against his black nationalist ideals.
For these reasons, the best answer is A.