I would say D.
In the expert, it states "since there was a population of about 37% blacks, it marks the first time a black mayor was elected from a predominantly white major city." This leads us to believe that not a lot of whites voted for blacks. Since this is the first time a majority of whites elected a black man as Mayor. Also, all the other options are stated in the excerpt, which means they are not assumed by the reader since it tells them.
I hope this helped. Have a great day!