Hello.
The most suitable option is C) Montgomery buses were forced to desegregate.
On December, 1955, Rosa Parks was seated in the coloured section of a bus, and refused to yield her seat to a white man in a bus. For these two reasons she was arrested. Later on, African- Americans start a boycott, sitting in the coloured section and refusing to yield their seats. On 1956, a Montgomery Federal court declared that segregation violated the 14th Amendment to the U.S. Constitution, and that all buses must be integrated.
Hope this helps.