The correct answer is B. scrollbar-arrow-color.
The scrollbar-arrow-color property is used to set the color of the arrow icon within a scroll bar. The other options are not correct because they are used to set the color of other parts of the scroll bar.
The scrollbar-base-color property is used to set the color of the base of the scroll bar. The scrollbar-darkshadow-color property is used to set the color of the dark shadow of the scroll bar. The scrollbar-face-color property is used to set the color of the face of the scroll bar.