(B) says, "It assumes without warrant that the qualities enabling a person to be elected to public office confer on that person a grasp of the scientific principles on which technical decisions are based."
The issue with (B) is that the argument never says that we should listen to Smith because she is the mayor; rather, it states that we should listen to Smith because she was formerly antinuclear. Thus, (B) is out.
Does this make sense? Let us know if you have any other questions!