A case can be made for all four answers being considered as reasonable. Yet, I think that Walker's essay moves closest to "the creative spirit."  Walker believes that modern African- American women have inherited the legacy of the creative spirit.  For Walker, these women possessed great narratives, amazing stories of courage, sadness, hope, and despair.  Had they been given the opportunities to share these stories as artists, there would have been a bevy of artistic contribution.  

While the creative spirit is the closest answer, a case can be made for African- American women absorbing the ability to work hard.  Walker phrases this condition as these women being "mules of the world."  This condition is one in which the ability to work hard, engage in persistence, and establish patience for their voice to be heard are all reasonable and logical extensions. However, it is this condition of the creative spirit that is the legacy that African- American women have inherited.  The ability to see themselves as artists of a real world is where Walker feels the responsibility for African- American women in the modern condition lies.