The correct answer is option B.
The issue that wouldn't concern most progressives would be racial segregation in the South.
Step-by-step explanation
Racial segregation is the separation of access to services, facilities, and opportunities of African Americans from white communities and also applies to general discrimination against them by white communities.
Taking into account that progressives despite unfair business practices such as monopolies, fight corruption and try to vanish child laborers, the fact that there is racial segregation in the South of the US wouldn't concern most progressives.