We're supposed to choose an option that is not mentioned in the passage. We choose option B because the rule was passed a year after the incident took place in 1955, where a black person could sit on any seat and it's suggested by the lines "On December 1955...Rosa was very tired...a white man ordered Rosa to give him her seat. Rosa refused...She was arrested and fined 14 dollars." This paragraph suggests that in 1955 a black person could not sit on any seat, it was roughly around a year later that they could. Hence we choose option B. Option A is mentioned in the line quoted from the passage "She didn't like it that black people had to use a rear door..." Similarly, option C has already been mentioned in the passage "black people had to use the rear door and sit at the back of the bus". Option D is also mentioned in the passage "She also didn't like the fact that she was required to give up her seat to a white person when the bus was crowded, so we don't choose it. All the events in A, C and D were true in 1955, hence we don't choose these options.